The relationship for synchrotron radiation infrared beamline between the aberration of symmetric optical system formed by two toroidal mirrors with the same optical parameters and pantograph ratio of the toroidal mirrors is analyzed. Computation results show that toroidal mirror with 3∶1 compression ratio can optimize the infrared beamline transmittance of chemical vapor deposition (CVD) windows to 50% at the working wavelength of 500 μm on the Synchrotron Radiation Infrared beamline BL06B at Shanghai Synchrotron Radiation Facility. The ray trace results by the optical design software Zemax show that the aberrations of the symmetrical structure do not affect the aggregation performance of the infrared beamline. Synchrotron Radiation Workshop simulation results show that the photon flux obtained with a pair of three times compression ratio toroidal mirrors and a diameter of 15 mm CVD diamond window is equal to a pair of 1 time compression ratio toroidal mirrors and a diameter of 45 mm CVD diamond window, while the former carbon peak absorption is about 37% of the latter. The symmetric optical structure formed by two toroidal mirrors with 3 times compression ratio can be used to optimize the performance of the SRIR beamline in the far infrared wave band, while the performance in the near and middle infrared wave band are also take into account.