Abstract: Due to the large interference of white noise at small strains and the asymmetric loop with large strains, the current methods cannot accurately calculate the soil dynamic modulus. The least square method is used to calculate the dynamic modulus of the soils under small strain, and the Kumar method is modified by the adjustment coefficient to calculate the tensile and compression modulus under large strain. The results show that compared with the traditional hysteresis loop method, the least square fitting method can effectively overcome the influences of white noise on the dynamic modulus at small strain, and make the tested strain range of the dynamic modulus in the dynamic triaxial tests wider. The modified Kumar method can well calculate the tensile and compression moduli of the soil under strong nonlinearity case, and it is perfectly connected with the fitting results of the least square method.