This paper aiming at the problems of incomplete data tomography with sparse rays in seismic tomography and explosion field reconstruction, analyses 3 factors which will influence tomography results, that is system layout, initial model and prior information. This paper presents the indexes of system optimal layout, analyses the influence of initial model and prior information to tomography results. A velocity model of explosion is imitated and the inversion results are compared. A conclusion can be gained that system optimal layout, initial model rational selection and prior information sufficient utilization can help to improve inversion precision furthest in practical project. 