Abstract: Spirulina platensis mud was the residual product after the processing of Spirulina products, which had rich organic matter and nutrients. The co-composting process and product quality of Spirulina platensis mud and pig manure residue were studied to develop the high-quality organic fertilizer products with Spirulina platensis mud as the main raw material, so as to realize the purpose of resource utilization of Spirulina platensis mud and pig manure compost. By using the Spirulina platensis mud as the main raw material and the pig manure compost after the solid-liquid separation from pig farms as the conditioner, the windrow composting method was adopted, and two groups of different treatments were set as C/N=25 (the treatment number was ZZ1) and C/N=30 (the treatment number was ZZ2), respectively. Furthermore, the changes of temperature, C/N, organic matter content, nutrient content (total N, total P₂O₅, total K₂O) and heavy metal content (Cu, Zn, Cd and Pb) in the composting process under two different treatments of C/N were studied. The results showed that the high temperature period of the compost under the treatments of ZZ1 and ZZ2 lasted for a long time. The days when the composting temperature was higher than 55℃ were 35 d and 42 d, respectively, and the days when the composting temperature was higher than 60℃ were 15 d and 24 d, respectively. The C/N of the two treatments gradually decreased and finally tended to be consistent, and the organic carbon content of ZZ1 treatment and ZZ2 treatment respectively decreased by 27.5% and 31.6% after the composting, indicating that the carbon source in the pig manure compost was easier to be decomposed and transformed by the microorganisms. During the composting, the total nitrogen, total phosphorus and total potassium increased with the decrease of organic carbon content, and the increasing range of total phosphorus and total potassium was larger. The contents of heavy metals (Cu, Zn, Cd and Pb) in the composting products of the two treatments increased after the composting. After 58 days of the composting, the contents of total nutrients and heavy metals Cd and Pb in all treatments met the requirements of NY 525-2012 'organic fertilizer'. The Spirulina platensis mud/pig manure compost could produce the high-quality organic fertilizer, and the composting product quality was better when the C/N of Spirulina platensis mud /pig manurecompost was 25.