The eigenmode characteristics for equilateral triangle resonator (ETR) semiconductor microlasers are analysed by the finite-difference time-domain technique and the Pade approximation. The random Gaussian correlation function and sinusoidal function are used to model the side roughness of the ETR. The numerical results show that the roughness can cause the split of the degenerative modes, but the confiJned modes can still have a high quality factor. For the ETR with a 3 μm side length and the sinusoidal fluctuation, we can have a quality factor of 800 for the fundamental mode in the wavelength of 1500nm, as the amplitude of roughness is 7.5 nm.