In the literature on the analysis of crustal deformation survey there exist some problems that need be clarified, Three of them are 1) Which approach is proposed for the estimation of deformation parameters, the "raw observation approach" or the "displacement approach"? 2) Will unique solution for deformation parameters be obtained from the displacement vectors with respect to different datums? 3) Is the present method justified, by which the displacement field of a free network is projected on a fault line to calculate the relative motions of the two sides of the fault? A11 these problems are surveyed in this paper. The mathematical model is first given of two epoch observations for crustal deformation analysis.Then, the paper makes some theoretical studies and provides numerical examples to answer the above questions.