The invention provides a method for improving saline-alkali land by utilizing a biological organic fertilizer. The method comprises the following steps of: classifying domestic waste; and composting kitchen waste, animal and plant debris and slurry from wastewater treatment. The application of the biological waste compost can obviously increase the organic matter and the mineral nutrients of alkali-hydrolyzable nitrogen, quick-acting phosphorus, quick-acting potassium, total nitrogen, total phosphorus, total potassium, and the like in saline-alkali land soil, accelerate the recovery and the reconstruction of a degenerated soil ecosystem, remarkably lower the pH value of the saline-alkali land, greatly increase the number of microorganisms in the saline-alkali land soil, strengthen the soil activity and speed up the land capability restoration. Through the invention, physiological active substances are generated to nourish and strengthen seedlings and fruits and stimulate the high yield and quality of crops; and the residual pesticides and fertilizers are degraded, the sugar degree is increased, the quality is improved, and nuisanceless and environment-friendly foods can be produced.