Target detection is one of the key technology of precision chemical application. Previously the digital coding modulation technique was commonly used to emit and receive the optical signal in the target detection systems previously in China. It was difficult to adjust the output power, and the anti-interference ability was weak in these systems. In order to resolve these problems, the target detection method based on analog sine-wave modulation was studied. The spectral detecting system was set up in the aspects of working principle, electric circuit, and optical path. Lab testing was performed. The results showed that the reflected signal from the target varied inversely with detection distances. It indicated that it was feasible to establish the target detection system using analog sine-wave modulation technology. Furthermore, quantitative measurement of the reflected optical signal for near-infrared and visible light could be achieved by using this system. The research laid the foundation for the future development of the corresponding instrument.