To study the specific mechanism of the impact of rural convergence of primary, secondary and tertiary industries on farmers' income increase, this paper selects panel data of 31 provinces and cities in China from 2005 to 2014 to test the threshold effect of rural convergence of primary, secondary and tertiary industries on farmers' income increase. It shows that in the model, human capital level in the countryside, rural recreation and sports investment in fixed assets, agriculture, forestry and fishing investment in fixed assets are threshold variables. In different intervals of different threshold variables, the promoting effect on farmers' income with the increasing level of rural convergence of primary, secondary and tertiary industries has remarkable difference. Human capital level in the countryside, recreation and sports investment in fixed assets, agriculture, forestry and fishing investment in fixed assets are unidirectional granger cause of the level of convergence. Therefore, the relevant departments should keep the agriculture, forestry and fishing investment in fixed assets at an appropriate level, cultivate new types of innovation talents and entrepreneurs in agriculture and enhance the integration of recreation, tourism and agriculture in order to improve the effect of rural convergence of primary, secondary and tertiary industries on farmers' income increase.