Chasing happiness is the ultimate goal of economic development and people’s lives. For a country with 550 million farmers, improving farmers’ happiness is particularly important. However, economic growth does not seem to make people happier. Most studies have explained this phenomenon from the perspective of income inequality, but there is a lack of identification of the impact of opportunity inequality, especially the research on the mechanism of the impact of opportunity inequality on farmers’ happiness. Based on this, this paper uses multiple mediating effect models to explore the relationship between opportunity inequality, social capital and farmers’ subjective well-being with CGSS data in 2013 and 2015. The innovation of this paper is that, firstly, based on the research of Bjørnskov（2006）, social capital is divided into two dimensions: social network and social trust, so as to reveal the relationship between opportunity inequality, social capital and farmers’ subjective well-being. More importantly, by dividing social capital into the two dimensions, we can identify which dimension plays a more important role. Secondly, we use a measurement of opportunity inequality which is different from previous studies. Previous studies have conducted a simple arithmetical average of income equity, educational opportunity and socioeconomic status to obtain the perceived index of opportunity inequality, which has two shortcomings: First, access to basic public services is particularly inadequate for rural residents, which has become one of the obstacles to equal opportunities. Therefore, if there is no evaluation of “access to public services”, the unequal level of rural opportunities cannot be fully and truly depicted. Second, the importance of each dimension is different, and a simple arithmetic average magnifies or diminishes the effects of each dimension. Therefore, we use the coefficient of variation method to weight each dimension. The main conclusions of this paper are as follows: （1）The expansion of unequal opportunities will reduce the subjective well-being of farmers, while social trust and social network will improve the subjective well-being of farmers.（2）When constructing the perception index of unequal opportunity, the negative impact of unequal opportunity on farmers’ subjective well-being will be underestimated if the dimension of “access to public services” and the weight of each dimension are not taken into account.（3）Opportunity inequality affects farmers’ happiness mainly through social trust, while the mediating effect of social network is not significant.