Abstract: Taking the 2-year-old Bambusa oldhamii under the Casuarina equisetifolia forest in the coastal sand field of Fujian Province as the research object, the water-retaining agent and nitrogen fertilizer test were carried out. The effects of different treatments on physiological indexes such as chlorophyll content of B. oldhamii leaves were determined. Principal component analysis and membership function method were used to comprehensively evaluate the effects of different water retention agents and nitrogen fertilizers. The results show that the application of water retaining agent and nitrogen fertilizer could improve the ability of B. oldhamii to resist the high temperature and drought in coastal sands of Fujian. The chlorophyll content is not significantly different in different treatment periods in summer. Soluble protein content, soluble sugar content, proline content, superoxide dismutase activity and peroxidase activity are the lowest in August, and highest in September. Malondialdehyde content and electrolyte permeability were the lowest in July and highest in August. Principal component analysis is used to screen out soluble protein content, soluble sugar content, proline content and malondialdehyde content as comprehensive evaluation indicators for water retention agent and nitrogen fertilizer application effect. Through the comprehensive evaluation of the membership function method, the average membership function values of A₂B₁ and A₁B₃ are the largest, and the comprehensive effect of the water retaining agent and nitrogen fertilizer treatment is better than other treatments.