Initial geostress is very important for the design and the construction of rock engineering. There are several methods based on finite element theory used to calculate geostress. According to measured geostress data obtained from Xiluodu Hydropower Station, the back analysis of initial geostress was conducted by means of neural network with the elastic finite element and the elastoplastic finite element. The results from back analysis of initial geostress with elastic and elastoplastic finite element calculations were compared. It indicated that the results from two schemes are very approximate, and they may simulate the regularities of distribution in the real geostress field. By further analysis, under natural condition, rock distortion is almost elastic except for little yield zone in surface. So in the low-mid geostress region, the result from elastic finite element calculation can reach the requirement of initial geostress back analysis.