Abstract: Adding reasonable constraint conditions to the observation equation can be used to conquer the ill-posed problem in the GPS water vapor tomography.In order to conquer the problem caused by the improper use of the weight matrix of the constraint equations,we apply the fitting method by selection of the parameter weights(FMSPW) to the GPS water vapor tomography.In this method,the parameter weight matrix is constructed based on the property of water vapor in the troposphere,and a simulation experiment is made to validate the feasibility of this method in the GPS water vapor tomography.The results show that the FMSPW can be used to get the reasonable distribution of water vapor.