Abstract: The basic principles and the corresponding algorithms of the finite volume method, the direct integral method and the Poisson equation method are introduced in detail, which are used to reconstruct the pressure fields based on PIV velocity fields. The instantaneous velocity fields of two incompressible flows, including the pipe flow with a sudden expansion and the flow around a square, are selected to study the influence of picture noise, velocity error, interpolation methods, the type and the precision of boundary conditions on reconstructed pressure fields by using different reconstruction algorithms. Finally, the transient pressure distributions of the pipe flow with a sudden expansion at 20ms are obtained by using the three algorithms respectively as well as the CFD. It shows that the finite volume method and the direct integral method are easily affected by noise to produce rude shocks, but maintain high accuracy in a larger range of error in velocity fields while they can get higher precision of reconstructed pressure fields with bilinear interpolation; the Poisson equation method isn't easily affected by noise so it produces few shocks, and has great advantages with the accurate PIV velocity fields while it can get higher precision of reconstructed pressure fields with bicubic interpolation; by measuring only several pressure points on the boundaries, the mixed boundary condition gets the accurate reconstructed pressure fields which are close to those of the Dirichlet boundary condition and far better than those of the Neumann boundary condition; the error of boundary conditions reduces the precision of reconstructed pressure fields, which is more severe than the error of velocity fields.