The stress path triaxial tests were conducted to examine the coefficient of K
0
of different stress paths and the undrained shear stress-strain under K
0
-conlidation.Formula of K
0
coefficient was proposed for K
0
overconsolidated soil.Based on anisotropic yield criteria
the undrained shear strength equations of K
0
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 K
0
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 K
0
coefficient with OCR.Experimental results indicated that the proposed formula has the advantage to predict the undrained shear strength of K