Abstract: A general shear strength formula of geotechnical space slip surface and a general relation between space failure surface position and strength criterion are proposed in the paper.It is obtained by theoretical analysis that geotechnical space slip surface is vertical with intermediate principal stress plane and the shear strength of geotechnical space slip surface relates only to vertical stress and Lode parameter.It provides theoretical basis for the determination of geotechnical space slip surface and has a guiding significance for studying geotechnical strength criterion.

Key words: space failure surface position, general shear strength formula