For efficient use of agricultural water, it is needed to know technical relationship between water and products. In other words, estimation of production function is necessary. Low variation in water usage data and limitation of yield calculation are two obstacles of estimation production function for pistachio orchards. In this study, one model was proposed for production function estimation, using vegetative and generative indexes of trees. Using stratified random sampling method, a sample of 286 owners of pistachio orchards in Anar and Rafsanjan city, Kerman province, was selected. The results showed that, in production function, in which pistachio yield is considered as dependent variable, determining optimal level of water using is not possible. For solving this problem, a production function was estimated, in which, vegetative and generative factors of trees were dependent variable. Using these functions, the optimal level of water consumption and EC were calculated 12000 cubic meters per hectare per year and 8500 micromohos per centimeter, respectively. Under these conditions, with existing orchard management, the average water use efficiency of the studied pistachio orchards is 131 g / m³. Different tests showed that estimated functions and calculated optimal levels are reliable. Also, a production function was estimated in which pistachio yield was dependent variable and independent variables were generative factors. This production function can be used for determination of pistachio yield, using generative factors every time during the year. At last, it is recommended that for determination of optimal level of water quality and quantity, a function was estimated, in which vegetative and generative indexes of trees are dependent variable. This method, increases research accuracy and decrease research costs.