Abstract：In numerical manifold method，fixed boundary is treated by penalty function method. The arrangement and value of penalty spring will affect the effect of numerical modeling；and work is complex. Based on the composition of displacement function on manifold element，a new method of constraints treatment of fixed boundary is proposed；and it changes the constraints treatment of fixed boundary into the constraints treatment of generalized node；and the constraints condition will be met strictly by using special cover function on physical cover；and then corresponding stiffness matrix is deduced. New method had been proved theoretically that it is correct；and it not only meets strictly the constraints condition in physical meaning，but it has simplified work of treatment. It is helpful for programming and the application of numerical manifold method to engineerings.
