Abstract: Nitrogen preserving agent is a kind of natural fixative that can control and improve the quality of compost. A 35 day aerobic composting experiment was conducted with chopped Alternanthera philoxeroides as raw materials, ferrous sulfate, sodium humate and calcium superphosphate as nitrogen preserving agents, in order to study the effects of nitrogen preserving agent on the composting process and nitrogen loss of Alternanthera philoxeroides. The physical and chemical properties, organic carbon, total nitrogen, total phosphorus and total potassium of the compost were monitored. The results showed that: during the high temperature period of compost, the composting temperature of nitrogen preserving agent treatment was significantly higher than that of CK, and the effect of ferrous sulfate treatment was the most obvious, which was more conducive to persistence of high temperature period. At the beginning of composting, the pH of compost decreased greatly in the group added with nitrogen retaining agent, and then the pH of the heap treated with nitrogen preserving agent was significantly higher than that of the control. After composting, the organic carbon and total nitrogen content of each experimental group showed a downward trend as a whole. Compared with the original material, the organic carbon content of each group decreased by 62.76%, 56.66%, 47.37%, 44.45% and 54.87%, respectively. Among the nitrogen preserving agents, the organic carbon content of the treatment group with humic acid decreased the most and the reaction speed was the fastest. The total nitrogen content of each group was decreased by 36.65%, 27.16%, 17.36%, 17.55% and 12.63%, respectively. The total nitrogen content of adding nitrogen preserving agent was significantly higher than that of aerobic bacteria and control group. The total nitrogen content of humic acid group was the highest, and the total phosphorus content of each group increased by 58.45%, 52.91%, 38.40%, 32.95% and 34.86%, respectively. The total potassium content was 2.00 times, 1.88 times, 1.29 times, 1.26 times, 1.15 times of the original materials respectively. The results indicated that the addition of superphosphate, ferrous sulfate and humic acid in the composting process of Alternanthera philoxeroides could accelerate the start-up speed, shorten the composting time and reduce ammonia volatilization. In summary, humic acid treatment was the best among the three nitrogen preserving agents.