注多元热流体组分含量的在线检测对调控稠油采收率有重要影响。阐述了多元热流体原位检测的长光程光路设计，研究了光束发散角对检测系统接收效率的影响，定量分析了注气管道高温内壁的杂散辐射强度，利用蒙特卡洛光线追迹法验证了离轴接收系统杂光抑制结构的有效性。结果表明，反射镜镀膜为银膜，光学窗口材料为熔融石英，多次反射结构的最佳反射次数为42次，有效吸收光程为220 cm；系统接收效率随发射光束发散角增大而减小，当发散角控制在1.8 mrad内，光学接收效率大于40%；在杂光入射离轴角为5°时，系统PST仅为5.66×10-8，当离轴角大于10°时，PST维持在10-14数量级以下，可有效抑制高温注气内壁对系统信号接收的干扰。

The species content detection of multiple thermal fluids (MTF) for heavy oil thermal recovery is noticeable effect on recovery efficiency. A long absorption path-length optical path design for MTF in situ detection was illustrated. The effect of the beam divergence on the receiver efficiency was discussed. The quantitative analysis of stray radiation irradiance was conducted and the stay radiation suppression performance of off-axis receiver was verified by Monte Carlo ray tracing method. The results show that when the reflector coating is silver and optical window material is fused silica, the best reflection times is 42 and effective absorption path length is 220 cm. The system receiving efficiency decreases with the increasing divergence angle of the emitted light beam, the optical receiving efficiency is greater than 40% when the divergence angle is controlled with in 1.8 mrad,. The point source transmittance(PST) is only 5.66×10-8 under the off-field angle is 5° and it can be lower than 10-14 when the off-field angle is larger than 10°, which can effectively suppress the interference of high temperature injection inner wall on system signal reception.