A weak optical signal detection lens is designed by optical design software – ZEMAX.The optical system requires small distortion and large relative aperture, which can match with the near-infrared CCD image sensor, in order to realize real-time, fast, high-precision detection of the weak singlet oxygen signal. The optical system parameters are relative aperture 1∶0.86, semi-image high 6.3 mm, spectral range(1 250～1 290 nm), magnification 1X, distortion＜0.1%, and manual focus. On the other hand, the mechanical structure of the optical system is design using the software-Auto CAD. The symmetrical structure is used to reduce costs and independent filter switching mechanism to facilitate the adjustment of the experiment. The detected lens successfully collects better weak singlet oxygen signals in the research experiments.