In order to determine the optimal irrigation method and biochar application rate for peanut, field experiments were conducted in Fuxin Mongolian Autonomous County Experimental Station of Northwest Liaoning Province for two consecutive years from 2018 to 2019. In this experiment, Xiaobaisha 1016 peanut was used as the material, and the split plot design with two factors was used, the main plots included three irrigation methods: furrow irrigation (F), drip irrigation (D) and mulched drip irrigation (M), the subplots within each of main plots included four biochar application rates: 0t/hm2(B0), 10t/hm2(B10), 20t/hm2(B20) and 40t/hm2(B40). The effects of different irrigation methods and biochar application rates on soil available phosphorus content, peanut root morphology and phosphorus accumulation were studied. The results showed that there was a significant interaction effect between irrigation method and biochar application rate. The highest yield of 10t/hm2 biochar was obtained under mulched drip irrigation, and the average yield increase in two years was 142%. Biochar could effectively promote the optimization of peanut root morphology, and the application of 10t/hm2 biochar under mulched drip irrigation could significantly increase the root length, root surface area and root volume. Compared with no biochar application, 10t/hm2 biochar application significantly increased the available phosphorus content and plant phosphorus accumulation, and the coupling effect of mulched drip irrigation with 10t/hm2 biochar application was the most obvious. Therefore, MB10 treatment was the best coupling mode in this experiment. This mode can give full play to the interaction effect. By creating a good peanut root morphology, increasing the available phosphorus content in the surface soil, and then promoting the absorption and accumulation of phosphorus by plants, and finally achieving peanut yield increase.