To address the serious problem of thermal accumulation in high power quantum cascade lasers,the optical and thermal performance of high power quantum cascade lasers with 4 W continuous optical output from a single tube in medium wave is designed and optimized based on the process method of MBE and MOCVD combined with secondary epitaxial growth of InP based quantum cascade laser structures in this paper.The device structure is modeled by COMSOL software,and the optical and thermal structural models are designed to analyze the effects of different structural parameters on the device performance,and the optimal structural parameters are obtained:In0.53Ga0.47As layer thickness of 50 nm,waveguide lower cladding InP of 1μm,upper cladding InP of 2μm,and encapsulated gold layer thickness of 3μm,the device has the best combined optical and thermal performance,where the waveguide optical limiting factor is 0.74 and the core region temperature is 378 K.The results of this study can provide guidance for the structure and process design of subsequent high power medium wave quantum cascade lasers.