[Background] As a soil modifier, biochar can improve soil fertility, promote arbuscular mycorrhizal (AM) fungal colonization, plant growth and development. [Objective] To evaluate the effects of AM fungi inoculation with adding biochar on the fertility of continuous cropping soil, and the growth of watermelon plants. [Methods] A pot experiment was conducted with watermelon continuous cropping soil as the substrate for planting ‘Yuanjia’ watermelon (Citrullus lanatus) grafted on the root stock ‘Quannengtiejia’ pumpkin (Cucurbita maxima×C. moschata). A total of 8 treatments were designed with the inoculation with or without AM fungi (Glomus versiforme), being added 0%, 1%, 2% and 4% biochar. The soil physical and chemical properties, soil enzyme activities, soil microbial quantity and the plant growth were measured. [Results] G. versiforme inoculation with biochar addition could significantly promote the formation of large soil aggregates and the mineralization of soil organic matter; stabilize soil pH; increase the number of soil bacteria and actinomycetes, and reduce the number of fungi; increase the activities of soil invertase, hydrogen peroxide enzyme and urease; activate soil mineral nutrients, and ultimately promote the growth and development of watermelon plants. Among them, the effect of inoculating G. versiforme and applying 2%?4% biochar combination is the best. There were interactions between AM fungi and biochar, which improved the continuous cropping soil pH, saturated water content and porosity, reduced the soil bulk density, favorable for the formation of large particles aggregate of soil, increased the soil enzyme activities and improved the rhizosphere soil microbial composition. [Conclusion] The combination of AM fungi and 2%?4% biochar can significantly improve the fertility of continuous cropping soil.