Surface model tomographic inversion is a kind of nonlinear model inversion technique. Using traveltime and path of seismic initial wave to inverse the velocity structure of media, it is not constrained by longitudinal and transverse variations of surface and near-surface structures. On the basis of the error caused by the difference between forward initial time and practical initial time, the velocity model is revised and, through repeated iteration, the error precision required can be attained. In working out static correction, the beam method is adopted to calculate the traveltime between the shot spot and the detection spot. In this way, the datum level correction quantity can be obtained.