Abstract: In order to explore the effects of iron-modified and phosphorus loaded biochar application on phosphorus utilization and yield of peanut plants under film mulching, a split plot pot experiment was carried out in 2021 and 2022 to evaluate the effect of iron-modified and phosphorus loaded biochar treatments (P1C0, conventional phosphorus application rate plus non-biochar treatment; P2C1, 3/4 conventional phosphorus application rate plus 7.5 t/hm² iron-modified and phosphorus loaded biochar treatment; P2C2, 3/4 conventional phosphorus application rate plus 15 t/hm² iron-modified and phosphorus loaded biochar treatment; P3C1, 2/3 conventional phosphorus application rate plus 7.5 t/hm² iron-modified and phosphorus loaded biochar; P3C2, 2/3 conventional phosphorus application rate plus 15 t/hm² iron-modified and phosphorus loaded biochar treatment) on chlorophyll content, net photosynthetic rate, dry matter accumulation, phosphorus utilization, soil available phosphorus content, and peanut yield under different mulching methods (M0, no mulching; M1, film mulching). The pot experiment was conducted at the Crop Drought-Resistant Cultivation Experimental Farm of Liaoning Academy of Agricultural Sciences, which was equipped with rain shelter to control the soil water content during the peanut growing season. The peanut cultivar for the experiment was “nonghua 9”. The biochar used for making iron-modified and phosphorus loaded biochar was derived from corn straw, which was produced by Shenyang Longtai Biological Engineering Co., LTD. During the whole peanut growth stage, when the soil water content was less than 55% (v/v) of the field capacity, the pot was watered until the soil water content reached to 85% (v/v) of the field capacity. The results showed that the M1 treatment increased the chlorophyll content and net photosynthetic rate at the seedling, flowering, pod setting, and pod filling stage by 7.6% and 29.1%, 12.4% and 25.9%, 14.9% and 16.0%, 6.5% and 14.8% (2 a average), respectively, compared to the M0 treatment. Dry matter accumulation at the pod filling stage and peanut yield of the M1 treatment were increased by 17.7% and 18.8% (2 a average), respectively, compared to the M0 treatment. Regardless of the film mulching methods, the net photosynthetic rate and soil available phosphorus content increased firstly from the seedling to flowering stage, and then decreased from the flowering to pod filling stage. Compared with the P1C0 treatment, P2C1 treatment increased the soil available phosphorus content, plant phosphorus accumulation content, dry matter accumulation content at the pod filling stage by 13.5%, 14.3%, and 6.5%, respectively, and increased the peanut yield by 10.2% (2 a average). Among the different film mulching and iron-modified and phosphorus loaded biochar treatments, the M1P2C1 treatment obtained the highest soil available phosphorus content and dry matter accumulation at the pod filling stage, and the highest peanut yield, which was 40.4% (2 a average) higher than the M0P1C0 treatment (conventional phosphorus fertilizer management). Therefore, the combination of film mulching and 3/4 conventional phosphorus application rate plus 7.5 t/hm² iron-modified and phosphorus loaded biochar treatment can improve the soil phosphorus availability and promote the phosphorus uptake by plants, thus increasing chlorophyll content, which lead to enhanced photosynthesis and dry matter accumulation, and finally increase peanut yield. The results can provide theoretical reference for phosphorus fertilizer reduction and efficient production in peanut field.