Abstract: In this paper,the effect of troposphere zenith delay estimation method on PPP data processing is studied.The results show that the horizontal gradient consideration can improve PPP precision to some degree.ZWD estimation with piece wise linear method is more or less better than with the piece wise constant method.If the piece wise linear method is adopted and the horizontal gradient is considered at the same time,ZWD estimation from static PPP is better than 5 mm.The horizontal accuracy is at the level of millimeter.The vertical accuracy reaches 1cm.To the accuracy of kinematic PPP,the horizontal accuracy is about 1cm and the vertical accuracy is about 2 cm.