The agricultural informatization contribution rate is the proportion of the contribution of agricultural informatization to the algebraic summation of agricultural economy growth accounting for the agricultural economy growth. It is a comprehensive index which reflects the function of agricultural informatization in enhancing agricultural productivity and agricultural economy development. This paper combines the analysis of the composite index with C-D production function to measure the contribution rate of agricultural informatization. Firstly this paper is going to establish the agricultural information evaluation index system including the infrastructure, resources, application, personnel, and policy environment. Then it is going to calculate each index and the composite index of agricultural informatization by means of synthetic rating analysis. Based on the above, this paper is going to build up a C-D production function model to measure the agricultural informatization contribution rate by regression function.