This research is based on the optimal control theory to establish the dynamic model of investment for analysing the efficiency of capital investment among the different patterns of cultivated farms and size of farms. Data used for this paper mainly comes from continuative record-keeping farm families, such as rice, fruit, and multi-crop farms in Taiwan from 1972 to 1991. The finaly results shown that the investment behavior of rice farms is too conservative, fruit farms are over invested and multi-crop farms exhibit high variations in investment. There is an inverse relationship between investment behavior and real interest rate. 2 to 7 years for adjusting from real investment to optimal capital stock are needed for all farms. From the analysis of elasticity, the characteristics of Le Chaterlier Principle are very significant in individual farm. The most important positive factor which affecting farms' optimal capital stock is the wage rate, and the negative factor is the price of intermediate inputs for both different patterns and size of farms.