Investigation tinder field, microplot and pot experiments for the effect of phosphorus fertilization on VA mycorrhizal response were conducted under unsterilized soil conditions. It was indicated that 8 jin P₂O₅/mu (60 kg/hectare) in form of superphosphate was the most favorable P level for VA mycorrhizal infection in 4 types of fluvo-aquic soil in Huang-Huai-Hai Plain of North China. Under such P level both growth and P uptake of plants were promoted by myeorrhizal inoculation while the lag phase of root infection was greatly shortened.