Abstract: In the open-optic path tunable diode laser absorption spectroscopy(TDLAS) detection system for gas, due to the surface finish degeneration of corner reflector during production and using and the atmospheric transmission disturbance, the incident direction of echo signal and the optical axis of receiving lens are not strictly parallel, resulting in the decrease of the system detection sensitivity.Aiming at this problem, firstly the offset of convergence point with the incident direction of echo signal different from the the optical axis of the Fresnel lens was analyzed, then a secondary optical element consisting of a conical reflector and a parabolic reflector was designed and its parameters were optimized by TracePro software.Moreover, the condensing performance simulation under the deviation range of echo incident angle in -6° ~ 6° was carried out.The simulation results show that the receiving angle of the optimized optical receiving module is 4.9° and the optical efficiency is 78.24%, the condensing performance is obviously improved comparing to the independent Fresnel lens and Fresnel lens-compound parabolic concentrator(CPC), the optimized component is applicable to the actual detection process.