Abstract: The horizontal coefficient of subgrade reaction,Kh, plays a significant role in problems dealing with laterally or loaded piles, excavation and tunnel engineering. The calculation formula for the horizontal coefficient of subgrade reaction is derived from the principle of the flat dilatometer test. And the influence factors of Kh, such as the width and shape of foundation, the rigidity and plexibility of the foundation and the rate of loading are considered respectively.then,the values of Kh are obtained from the calculation formula according to the data of insitu DMT in Shanghai,and the calculated values of Kh are almost equal to those suggested in the code.