The gain of compress strained multiple-quantum-well（CSMQW） lasers is theoretically analyzed and calculated.The energy movement of the hole Fermi level and the variation of the differential gain in the condition of p-type modulation doping（p-MD） in CSMQW barrier is also discussed.The relationship between the linewidth enhancement factor（α） and compress strain

p -MD density and injection carrier density is evaluated.The results show that strain effect and large injection can reduce α-parameter

however

it’s difficult to make the zero-point of α- parameter penetrate to the gain region

while the use of the P-MD can effectively reduce α-parameter at some wavelength in the gain region to zero.The increase of compressed strain and injection carrier density can effectively improve the reduction of α-parameter caused by P-MD.