A mathematical model of the gait of the transtibial amputee based on the inverted pendulum model is presented, this model shows the gait affectation when the prosthesis components vary. The model for the lower limb with transtibial amputation is a triple pendulum with 6 segments and 7 degrees of freedom, the Lagrange theory to determine the equations of motion of the system was used. With the system's equations, simulation software to visualize the 3D animation of the patient in normal gait and with prosthesis was designed, also to kinematic analysis of the joints of the lower limb and the forces applied to the surfaces. Spatio-temporal data specific to gait are acquired and it is possible to vary the weight and height of the patient, lengths, diameters and materials of the prosthesis components, making it possible to carry out the analysis for different subjects.