In an open V-type system,by numerical results of differential equations,the physical mechanism of laser without inversion(LWI)was analyzed,and the effects of the probe and driving fields detunings,the Rabi frequencies of the driving fields,and the initial values of the populations on LWI transient were discussed. The conclusions show that the populations of the two levels coupled by the driving field have the same oscillation frequency,however,exist a phase difference π.The dispersion equals to zero and twophoton coherent item is real number when the driving and the probe fields are both resonant. Oscillation period of the gain,coherent item and population difference reduce with the increase of the Rabi frequencies of the driving field. The initial values of the populations mainly affect the oscillation amplitudes of the gain,coherent item and population difference but don't affect their values in the steady state.