The study shows that:When there are detunings of the probe and driving fields,the variation of Doppler width has an obvious effect only on the maximum of the invesionless gain,which decreases rapidly with Doppler width increasing;when there is a probe-detuning and the driving field is resonant,the system can get an extreme value of maximum of the invesionless gain when Doppler width takes a suitable value;the extreme values increase with the ratio of the atomic injection rates increasing;the higher the degree of the frequency up-conversion attains the extreme value is;the effect of Doppler broadening on the gain in an open ladder-type lasing without inversion(LWI) system have some obvious differences from those obtained from other LWI systems.