Abstract: Polybutylene adipate terephthalate (PBAT) has emerged as a potential biodegradable mulching film in recent years. Taking the tomato cultivation as the research object, three treatments were selected for the biodegradation characteristics, including the ordinary PE mulching film (T1), PBAT/ straw-based biodegradable mulching film (T2), and non-mulching film (T3) in Jiangsu Province of China. The microstructure, morphology, and mechanical strength of the film were characterized during degradation. Meanwhile, the effects of mulching film on the tomato plant height, stem diameter, and yield were clarified to determine the comprehensive benefits of biodegradable mulching film. The results show that there were a series of changes in the physical and chemical properties of the PBAT/straw-based biodegradable mulching film during the 120 d mulching period. The Fourier infrared spectrum showed that the molecular chain of the degradable mulching film was broken under the action of soil microorganisms, light, and water. The X-ray diffraction pattern exhibited that the crystalline area of degradable mulch was destroyed gradually, whereas, the amorphous area increased relatively. Thermogravimetric analysis indicated that there were a few Tmax changes, T0 increase, and a decrease in the carbon residue rate, indicating the thermal properties of the degraded mulching film. The water contact angle confirmed that the degradable mulching film was degraded in the field. Scanning electron microscopy (SEM) images illustrated that there was an uneven degradation of mulching film. The tensile strength and elongation decreased gradually at the break of the degradable film, as the film covering time increased. The mechanical property test verified that the PBAT/ straw-based biodegradable mulching film was degraded gradually in the field with a slow degradation rate after 120 days. Moreover, there was a better effect of degradable mulching film on the tomato growth, compared with the conventional PE and non-mulching film group, in terms of the plant height and stem diameter of tomato plants. The yield of tomato fruit in the degradable and the PE mulching group was equivalent to 667 m2, which was 13.5% and 15.0% higher than that in the non-mulching film group, respectively. The excellent ecological benefits and the higher recovery cost-saving were achieved for the PBAT/straw-based fully biodegradable mulching film, although the product cost was relatively high. In general, the PBAT/ straw-based fully biodegradable mulching film can be widely expected to serve a remarkable effect on tomato cultivation in the greenhouse. The degradation cycle can be further explored to accelerate the spread the promotion of the degradable mulching.