Bio-slow filtration water purification technology can effectively reduce the content of organic pollutants in water and improve the water quality by interception, filtration, adsorption and decomposition of sewage by filter materials and biofilms. The high content of organic matter is a prominent feature of rural domestic sewage. In order to improve the purification efficiency of rural domestic sewage by bio-slow filtration water purification technology, it is necessary to optimize the structure and performance of the filter materials and biofilms in the biology slow filter (BSF). The effect of different biofilm cultivation methods on the purification of rural domestic sewage by BSF were compared and analyzed by laboratory biofilm cultivation and BSF purification experiments. The results showed that the biofilm formed by artificial inoculation needed shorter maturation time and had stronger stability than that formed by natural cultivation at 25 ℃. However, there was no significant difference in the purification effect of sewage turbidity, ammonia nitrogen and total phosphorus by BSF with different biofilm cultivation methods after the maturation of biofilm, except the removal effect of organic matter (COD) in sewage by BSF with artificial inoculation biofilm, which was significantly better than that of BSF with natural cultivation biofilm. Both cultivation methods have good purification efficiency for rural domestic sewage, and all the effluent quality indicators meet the requirements of sewage discharge. The research results can provide technical reference for the purification treatment of rural domestic sewage.