Earthworm is a typical multi-body segment and soft-bodied animal. In this paper starting from a biomechanical point of view we analysis the tensile stress of the body wall during rest and peristaltic crawling and describes the deformation coupled with a simple friction model during peristaltic crawling. We calculate the body wall stress and crawling velocity for a certain range of mass of earthworms . The dynamic equation of earthworm crawling is presented and calculated numerically. Numerical results show that the mean speed of earthworm crawling for different mass is consistent with experimental value.