[Objective] The study aims to analyze the effect of bio-organic fertilizer on the supply of soil nutrient, the nutrient absorption by Bok choy, and vegetable biomass under the conditions of decreasing application of chemical fertilizer, and to provide theoretical basis for the practice of fertilizer-decreasing application. [Methods] We used the pot-test, with Bok choy as target species, to investigate the effect of bio-organic fertilizer and different amount chemical fertilizer mixtures on alkali-hydrolyzing nitrogen, rapidly available phosphorus, potassium on soil, and vegetable biomass and absorption of nitrogen, phosphorus, potassium by Bok choy. [Results] The bio-organic fertilizer could increase the supply of soil nitrogen, phosphorus and potassium in the limited period time if applying the mixture of both fertilizer. Furthermore, under the condition of the decreasing 15%～25% of conventionally chemical fertilizer application, the mixture fertilization technique did not affect the fertilizer supply of the soil, thus decreasing the non-point contamination of agriculture and stress of environment pollution. Bok choy growing test verified that under the decrease of 15%～25% of conventionally chemical fertilizer application, the mixture fertilization method did not reduce the biomass, and absorption of nitrogen, phosphorus, potassium of Bok choy, thus enhancing the utilization ratio of fertilizer. [Conclusion] Bio-organic fertilizer not only activate the soil available nitrogen, phosphorus, potassium, but also stabilize the supply.