ESPI (Electronic Speckle Pattern Interferometry) is a new technique that can be used to measure the density field or the temperature field of a transparent fluid. One essential part of this technique is to reconstruct a 3D image of the physical field by use of the projections of the field to different directions and/or different sections. This work introduces the primary principle of 2D reconstruction and then focuses on convolution method for parallel beams. On this foundation, it simulates the projections for double Gauss distribution function and reconstructs the simulating temperature field by the convolution method for parallel beam. In order to instruct ESPI experiment, it also simulates three different errors and gets the sensitivity of them. According to the limited direction character of ESPI, the double linear interpolation method is used and gets a better reconstruction result.