Abstract：A new method for calculating strains based on side length changes is proposed.By use of this method the strains distribution of Chinese mainland in the period of 1999 to 2001 are calculated. The results show that the analysis of the continuous deformation in the largescale and dense GPS velocity field can reveal not only the integral tectonic characters of Chinese mainland but also the tectonic deformation which have a mutation in the SouthNorth Seismic Belt and is stronger in the west than in the east and stronger in the south than in the north.The largest strain rates are found in the areas as Kunlun block,Xianshuihe fault zone and central Yunnan,and the variation of velocity is very rapid,and extensive strain is found in the eastern part of Tianshan.
