Based on an analysis of some theories, this paper studies the relationships among rural household investments and their interaction with farmer income increase empirically by the data of 1983-2005. The findings are: (1) Health investment makes against the growth of farmer, human capital investments for other types, besides, it can not satisfy the needs of farmer. (2) Although migration investment is useful to the growth of farmer income, education and health investment, its effects is time lagged. (3) Education investment has the biggest effects on the growth of farmer income; besides, it also reduces the cost of migration. However, this reduction is a bit small. Finally, some brief suggestions are put forward based on the analysis.