Abstract: In order to accelerate development of agricultural mechanization in Ningbo city of Zhejiang province，agriculture production function was presented in Ningbo city by Cobb Douglas production function and linear regression optimization according to statistic data from 1990 to 2010.Agricultural machinery contribution portion to agricultural output growth was estimated by means of production function above.Results showed that agricultural machinery contribution portion to agricultural output growth was 1137% in Ningbo city.Then mechanization level of farm work can raise by increasing of equipment level and optimization structure of agricultural machinery，agricultural mechanization contribution portion to agricultural production will be further enhanced.