Aiming at the low power consumption, miniaturization, integration and intelligence of water quality multi-parameter monitoring instruments, a micro-in-situ water quality multi-parameter detector based on the fusion of sequential injection analysis (SIA) and continuous spectral detection methods has been developed. The core of the system design lies in the structure design of the digestion cell and the digestion cell as the detection cell, and the principle design of the microinjection technology sequential injection platform and the design of the multi-parameter combined digestion measurement process. A multi-parameter sequential injection analysis and detection process based on the national standard for water quality testing was designed. Fusion sequential injection analysis technology was used to detect the content of nitrite nitrogen, nitrate nitrogen, total nitrogen and total phosphorus under the conditions of continuous spectrum scanning measurement. Before digestion, the nitrate nitrogen and nitrite nitrogen were measured by direct spectrum. After digestion, the total nitrogen is detected by spectrum, and after color reaction, the total phosphorus is detected by spectrum. In this system, the in-situ water quality parameters of nitrite nitrogen, nitrate nitrogen, total phosphorus and total nitrogen are used as measurement objects. Based on the continuous spectrum analysis and the least square method, the regression model is established and the concentration absorbance standard working curve of each parameter is drawn, and its goodness of fit (determining coefficient) is ≥0.989 9. Prepare the mixture solution with a known content of nitrite nitrogen, nitrate nitrogen, total nitrogen and total phosphorus. According to the above multi parameter detection process, use the standard working curve drawn by the system to measure four parameters. The experimental results show that the repeatability of experimental parameters (RSD≤3.86%), the system can stably and efficiently analyze the content of nitrite nitrogen, nitrate nitrogen, total nitrogen, and total phosphorus in different water samples. Based on the SIA continuous spectrum fusion method to study the in-situ water quality multi-parameter detection method, it plays an important role in improving the technical performance of on-line water quality monitoring instrument. Technical performance has an important role. The development of a miniature multi-parameter water quality monitor has a good prospect for parameter expansion and is suitable for a variety of water quality online monitoring platforms.