It is pointed out in this poper that the modulation of optical confinement factorin index coupled DFB lasers can give rise to the gum coupling effect.This effect is smallnear threshold region, but it increases when output POwer increases. The influence of thisgain coupling effect in λ/4 Phase Shifted DFB lasers on threShold gum and frequency shiftis in some way like spatial hole burning.The quantum size effeCt has little influence onthis gain coupling effect. Because the spatial hole burning is much small in MQW lasers, the influence of this gain coupling effect on the threshold gain and frequency shift in MQW lasers will be obliviously.