This study took Spirulina platensis as the experimental object to explore the effects of nitrogen concentrations (5, 15, 30 and 45 mmol·L^-1) and phosphorus concentrations (0.5, 1.5, 3.0 and 4.5 mmol·L^-1) on the growth, metabolites and chlorophyll fluorescence parameters of immobilized S. platensis, so as to provide a theoretical basis for large-scale and efficient cultivation of Spirulina. Results showed that: (1) with the increase of nitrogen and phosphorus concentrations in the culture medium, the biomass density and productivity of S. platensis increased first and then decreased, and reached their highest values at the nitrogen concentration of 30 mmol·L^-1 and phosphorus concentration of 3.0 mmol·L^-1. Low nitrogen and phosphorus concentrations affected the cellular structure of S. platensis, manifested as shorter single-cell filaments and fewer spirals, leading to the decrease of biofilm cell density. (2) Consistent with the S. platensis biomass, the content of photosynthetic pigments showed a trend of first increasing and then decreasing with the increase of nitrogen and phosphorus concentrations in the medium, and both reached the highest values at nitrogen concentration of 30 mmol·L^-1 or phosphorus concentration of 3.0 mmol·L^-1. (3) When the phosphorus concentration in the medium was fixed, the maximum light energy conversion efficiency (F_v/F_m) and electron transfer rate (ETR) of the PSⅡ reaction center of S. platensis increased with the increase of nitrogen concentration, and the lack of nitrogen affected the photosynthetic pigments synthesis, thereby weakening the photosynthesis of S. platensis. When the nitrogen concentration in the medium was fixed, the F_v/F_m and ETR of S. platensis showed a trend of first increasing and then decreasing with the increase of phosphorus concentration. (4) Although low nitrogen and phosphorus concentrations were not conducive to the increase of soluble proteins, they could stimulate the accumulation of soluble polysaccharides, and the more severe the limitation of phosphorus source was applied, the lower the protein content of S. platensis was produced, and the higher the polysaccharide content was accumulated. According to this study, the synthesis of high-value products such as Spirulina proteins and polysaccharides can be induced by adjusting the nitrogen and phosphorus concentrations in nutrients. Therefore, the synthesis and accumulation of corresponding target products can be promoted by adjusting the concentrations of nitrogen and phosphorus in production. The tolerance of S. platensis biofilm to nitrogen concentration was stronger than that of phosphorus concentration. The chlorophyll fluorescence parameters of S. platensis were higher under high nitrogen (45 mmol·L^-1) culture, and the biomass yield was also higher.