The economic loss and the threat to personal safety caused by the leakage of hazardous chemical gases in natural gas stations, mining, industrial chemicals, manufacturing, gas pipeline transportation and other places are huge. It is extremely necessary to strengthen the real-time monitoring and warning of such hazardous chemical gas leaks. However, traditional detection methods have defects such as slow response, high maintenance cost, low efficiency, the need for close contact sampling and testing, and the inability to monitor in real time. In recent years, tunable diode laser absorption spectroscopy has become a key technology for trace gas detection, with the advantages of fast measurement response and strong wavelength selectivity. In order to realize real-time, long-distance and non-contact monitoring of hazardous chemical gas leakage and to improve monitoring efficiency and accuracy, a multi-component trace gas remote sensing system based on wavelength modulation spectroscopy is proposed. The core of the system is based on STM32 chip combined with a self-designed driver circuit to control the laser, and the second harmonic signals of methane, ammonia and acetylene are extracted separately by using different modulation frequencies to realize simultaneous, real-time and long-distance detection for the mixed gases. We use wavelength modulated spectroscopy with light intensity modulation amplitude normalization to make the remote sensing results free from the influence of the echo laser on the signal intensity. By comparing the direct absorption signal and the second harmonic signal of the gas concentration detected by the system, it is verified that the wavelength modulation technique has a significant noise suppression effect and can greatly improve the detection sensitivity and detection distance. Through calibration experiments, the measurement accuracy and lower detection limits of the system are evaluated. The experiments have shown that the lower detection limits of the system can reach 87 ppm·m, 212 ppm·m and 12 ppm·m for methane, ammonia and acetylene, respectively, and the measurement error is less than 10%. We tested the remote detection performance of the system over long distances, and the results showed that the remote detection distance can be up to 40 m. The system provides a multi-component, real-time, synchronous, high-sensitivity, long-distance and stable performance remote sensing solution for the research and application of laser trace gas detection, which can be widely used in gas monitoring and early warning of mine disasters, gas leakage monitoring and early warning of hazardous chemical field stations and transportation pipeline networks.