Abstract: Compared with the traditional combined planar V-H-M loading,the non-planar V-H-M loading which is more accordant with the actual loading condition of foundations for offshore wind turbines is considered by the Φ_H-M（angle between the horizontal load H and the moment M）. The results show that with the decrease of Φ_H-M,the H-M failure envelope of bucket foundation shrinks remarkably in the first quadrant and expands gradually in the second quadrant,and finally presents symmetry. The reduction of combined bearing capacity of bucket foundation due to the Φ_H-Mcannot be neglected. Based on the results,expressions which can determine the failure envelopes of bucket foundation under combined planar and non-planar V-H-M loading are proposed and the effect of Φ_H-Mon the combined bearing capacity is clarified. An example is given to present the applications of the expressions and the failure envelope theory.