In this study, humic acid (HA) and polybutylene succinate (PBS) were compounded by melt blending to prepare a HA/PBS composite mulch. The compound was subjected to three conditions by placement in direct sunlight (on the soil), in the soil, and in the shade of plants. The crystallization performance, thermal performance, mechanical properties, degradation performance, and water vapor transmission rate of the mulch film at 21, 42, and 63 d, and the effect of the HA/PBS composite mulch film on the growth of lettuce, were studied. The crystallization experiment showed that in the three cases, the crystalline form of the composite mulch film was not affected by time, but the degradation by other factors caused the crystallinity of the film to decrease. The positional variables had little effect on the thermal performance. Analysis of the mechanical properties showed that the tensile strength and elongation at break decreased for the films subjected to all conditions. Analysis of the degradation performance and water vapor transmission rate showed that the composite mulch film degraded fastest when shaded by plants, followed by that in the soil, and was the slowest under exposure to sunlight. Evaluation of the effect of the compound mulch film on the growth of green vegetables showed that the film can promote the synthesis of chlorophyll, peroxidase, and vitamin C in the leaves of lettuce and inhibit the production of malondialdehyde. •Prepared functional nutrient HA/PBS biodegradable agricultural mulch.•The HA/PBS mulch film has a good comprehensive performance and is easier for water molecules to penetrate.•The mulch film has a good promoting effect on the growth of green vegetables.