We use the model of noninversion lasing in an open type three level system,start from the equations of the atomic density operator,discuss the effects of detunings of the driving and probe fields on the laser gain and refractive index under steady state case.The theoretical analysis shows that:If the Rabi frequency of the driving field is smaller,the gain can reach a maximum only when the probe field is resonant;the non absorption high refractive index can be obtained by adjusting the detuning of the probe field.When the Rabi frequency of the driving field is larger and reach a threshold,a special gain region will appear by adjusting the detuning of the probe field.The detuning variation of the driving field will have a more obvious effect on the refractive index than on the gain.the special gain region in the latter.