With the development of economic globalization and the increasing competitiveness of Chinese enterprises, more and more Chinese enterprises have gone abroad and achieved rapid growth through overseas M&As. Under the background of the ever-expanding scale of overseas M&As, the economic effects of overseas M&As have become an issue of increasing concern to all parties. However, because Chinese companies started overseas M&As lately, they lacked sufficient experience when dealing with business and organizational conflicts caused by factors such as cultural differences, institutional differences and geographical distances, which led to turmoil in business and organizational structure after overseas M&As. This will bring greater uncertainty to the business integration and organizational restructuring of Chinese companies. The uncertainty brought by overseas M&As may distorts investment decisions and reduces the investment efficiency. Therefore, this paper attempts to answer the question: do overseas M&As reduce the investment efficiency, in order to analyze the economic effects of overseas M&As from the perspective of corporate investment efficiency?　　The article uses the data of listed companies that implement overseas M&As from 2012 to 2016, combined with the propensity-score matching approach and the difference-in-differences estimation method to study the impact of overseas M&As on corporate investment efficiency. In order to test the specific performance of overseas M&As affecting corporate investment efficiency, the article further divides investment efficiency into two aspects: over-investment and under-investment, and examines the impact of overseas M&As on these two types of non-efficiency investments.　　The study finds that: （1） overseas M&As have a negative impact on corporate investment efficiency, and this reduction is mainly reflected in the over-investment behaviors rather than the under-investment behaviors; （2） from the perspective of ownership, the investment efficiency of SOEs and non-SOEs has been negatively affected in the short term. In the long run, the investment efficiency of SOEs is still negatively affected by overseas M&As, while the investment efficiency of non-SOEs is positively affected by overseas M&As; （3） from the perspective of the host country, the overseas M&As of the target countries in developed countries （regions） have reduced corporate investment efficiency. The overseas M&As of the target countries in non-developed countries （regions） have no impact on the corporate investment efficiency.　　The conclusions reached in the article have obvious policy implications. At present, some enterprises do have the phenomenon of inefficient investment by overseas M&As. This question urgently requires regulators to analyze and judge, and formulate practical measures to identify and treat overseas M&As behaviors. Under the conditions of controlling overall risks, regulators should encourage enterprises to make reasonable foreign investment and support overseas M&As with the purpose of promoting domestic industrial structural upgrade and technological progress.　　In a word, the contribution of this article is reflected in three aspects. First, from the perspective of the uncertainty of overseas M&As, the paper analyzes the analysis framework of overseas M&As affecting corporate investment efficiency, and enriches the economic effects of overseas M&As. Second, by matching the Zephyr global M&A database and CSMAR database, and using the propensity-score matching approach and the difference-in-differences estimation method, this article not only tests the negative effect of overseas M&As on investment efficiency, but also explores the difference of the effect of ownership and the host country. Third, at the conclusion, although overseas M&As have a negative impact on investment efficiency in general, the negative impact on SOEs is significantly stronger than that on non-SOEs, which provides a theory for the adjustment of high-quality development strategies and current overseas M&As policies.