In this paper,the relative dielectric constants,the elastic compliance constants and the piezoelectric strain constants of KH2PO4(KDP)crystal have been determined by the LRC bridge,resonant method and the interferometric method respectively,and these parameters have been compared with those of the literature values.The measured elastic coefficient s11 and the elastic stiffness coefficient c11 are 3.11×10-11m2/N and 4.6×1010N/m2 respectively,which are different from the values reported in the literature.The measured piezoelectric strain constant d14 is 9.51×10-12C/N,thus the value reported in the literatures has been corrected.The other values of electro elastic constants determined in this test are consistent with the literatures.