The stress path triaxial tests were conducted to examine the coefficient of K0 of different stress paths and the undrained shear stress-strain under K0-conlidation. Formula of K0 coefficient was proposed for K0 overconsolidated soil. Based on anisotropic yield criteria, the undrained shear strength equations of K0 overconsolidated soil were developed. The validity of proposed procedure was verified by comparing calculated results and experimental results. The results indicated that the formula proposed by Mayne and Kulhawy overestimated the coefficient when the OCR was large. The undrained shear strength equations of K0 overconsolidated soil avoided errors which were caused by assuming a constant slope of rebound denoted by the effective overburden pressure, by considering the variation of K0 coefficient with OCR. Experimental results indicated that the proposed formula has the advantage to predict the undrained shear strength of K0 overconsolidated soil.