The present upper-bound method of limit analysis has many self-contradictory conceptions in theory although its results are reasonable. For example

the associated flow rule is often used at present

but it is shown by experiments that it doesn’t adapt to geotechnical materials; the volume deformation which is larger than real deformation is produced in calculating

but it is assumed to be constant in classical analyzing theory; the velocity slip line is the same as the stress characteristic line according to associated flow rule

but an angle between the two lines is adopted in analyzing; the shear stress and normal stress exist simultaneously in every point of slip surface

but the friction work is not reflected in process of limit analysis. The scientific theory of the limit analysis method about the geotechnical materials is given by the generalized plastic mechanics theory

which thrives in China at the present years. The upper-bound method of limit analysis based on the generalized plastic theory is given in the paper

so these self-contradictory conceptions can be avoided completely and the right solutions are gained. To compare with the classical method

it is proved that the results of limit analysis solutions gained by two methods are nearly the same. The classical method can be used as a practical method since it is simple to solve questions. A systematic analysis and comparison of the above two limit analysis methods is given

and the sameness and un-sameness between them are clarified.