In traditional semiconductor lasers,it is usual to obtain single lateral mode operation by narrowing the ridge of waveguide,which is sensitive to fabrication inaccuracies.To overcome this shortcoming,a quasi-PT (parity-time)symmetric double ridge semiconductor laser is proposed to reach single lateral mode operation for an intrinsic multi-mode stripe laser.The coupled mode theory is used to analyze the non-Hermitian modulation of the gain (or loss) of the PT symmetric double ridge laser to obtain the coupling coefficient between the two ridge waveguides.Finally,the mode field distributions of the quasi-PT symmetric double ridge laser are simulated before and after the spontaneous PT symmetry breaking,which keep the laser operating in single lateral mode.