This paper introduces the design of a high-precision instrument for strain sensors, which accuracy class is 0.0005. In order to reach that high accuracy AC excitation voltage with 225Hz frequency, pulse width modulation multi-slope integration and high-precision voltage reference are developed. To verify the consistency of the measurement accuracy and uncertainty of the instrument, the comparison test of the DMP9000H high-precision instrument and the DMP41 high-precision instrument (made by HBM Germany) is carried out in two research institutions, the comparison results show that the relative deviation between DMP9000H and DMP41 measured at the comparison point is within ± 0.0005%, and the relative expanded uncertainty of DMP9000H measured at the comparison point is 1.0 × 10-5 (k = 2); |E_n| of the measurement results of each comparison point are less than 0.5, which indicates that the difference between DMP9000H and DMP41 is within reasonable expectation, and the comparison result is satisfied.