Encapsulation through polymeric membranes to control the release rate of fertilizers can reduce fertilizer's losses and minimize environmental pollution. A biodegradable starch/polyvinyl alcohol (PVA) blend film for coating the soluble granular fertilizer has been prepared. The influence of the blending ratio of starch/PVA and the content of formaldehyde on the properties of the film has been investigated. The membrane (si:arch:PVA =7:3, crosslinked by formaldehyde content:10wt%) structure was observed by X-ray diffraction (XRD), Fourier transform infrared absorption spectra (FTIR), and atomic force microscopy (AFM). The XRD results shows that the crystal structure of PVA was changed after being crosslinked with starch, whose vice-bond was broken and crystal was destroyed. The FTIR explores the starch was linked with PVA by chemical binding the crosslinking reaction results in an improvement of compatibility of the starch/PVA blend films. The AFM results show that the films' surface became level and smooth due to the crosslinking reaction with the application of formaldehyde. The starch/PVA blend films could biodegrade in the soil environment.