Abstract：The seismic response capacity of Sacks borehole body strainmeter was researched. It is discovered that the capacity is connected with eathquake magnitude or epicenter distance and spread along a line. The law is found that the amplitude will increase exponentially when earthquake magnitude increase and it will decay with power function when the epicente distance increase. The characters of the conseismic strain step of 6 Sacks body strainmeters in Beijing and Tianjin were analysed. It shows that there is a certain relation between the strain step’s polarity （press and spread） with the faults which the observation stations are located on.
