The key issue of GPS height transformation is the calculation of the height anomaly. In this paper an improved method for GPS height transformation in mountain area is presented. First, the weakness of the existing formula for height anomaly calculation is pointed out. Then, a continual integral formula (called CIFHAC) is derived. Because human's interference is not needed, the formula proposed in this paper is free of artificial errors. The influence of different reference heights in mountainous and/or huge mountainous areas on the calculation values of height anomaly is analysed by means of trials.Furthermore, a new heightfitting model with additional parameters is proposed. The result of the trials shows that, due to the mentioned improvement, the precision of the height fitting is enhanced and that the new model is more suitable for GPS height transformation in mountain areas. The theoretical model is used in GPS height surveying in the job site and comparison is made with the actual height.