Stable dual-mode lasing semiconductor lasers can be used as a seed source for photonic generation of optical frequency comb and terahertz carrier. Normal square resonator microlasers can support dual-mode lasing with frequency interval up to 100 GHz. Here we demonstrate ultrahigh $Q$ deformed square resonators with the flat sides replaced by circular sides for further increasing transverse mode intervals. The stable condition of dual-mode lasing is verified based on nonlinear gain analysis. Furthermore, the beating signals of 0.43, 0.31, and 0.16 THz are obtained by the autocorrelation measurement, which indicate the deformed microlasers as an architecture for THz radiation generation. The deformed square resonators pave the way for controlling the lasing spectrum and serve as ultrahigh $Q$ microresonators for photonic integrated circuits.