Panel model is used to make empirical analysis of the economic effects of agricultural credit investment in west China during 1978-2009, results show that the effect of agricultural credit investment on promoting agricultural output increase is obvious but its effect on promoting rural inhabitants income growth is relatively weak, that the output elasticity of agricultural credit capital is gradually improved, that the response of agricultural output to credit investment should be more active, that agricultural output and rural residents income are not sensitive to the change of agricultural credit interest rate, that credit ration phenomena in rural financial market are still popular and that the economic effect of agricultural credit investment is varying between different provinces. Thus, the economic effect of agricultural credit investment can be enhanced by perfecting credit mechanism of agricultural loan, by increasing effective supply for agricultural loan capital and adjusting investment structure, by adjusting agricultural production structure in west China and by improving peasants income structure.