In order to improve the application potential of polylactic acid insulation materials in electrical insulation and other fields, the effects of methyl methacrylate-butadiene-styrene (MBS) and silk fiber on the properties of MBS/SF/PLA composites were systematically studied. The experimental results show that MBS significantly improves the impact strength, but with the increase of MBS content, the bending strength gradually decreases. However, when the MBS content was fixed at 13 wt%, the silk fiber content increased from 2 wt% to 4 wt%, and the bending strength of the material increased from 72.45 MPa to 84.88 MPa, an increase of 14.64%. The rigidity and strength of the whole material are improved without significantly reducing the impact performance. Through the breakdown voltage test, it is found that the content of MBS affects the insulation performance, and increasing the content of silk fiber is helpful to improve the insulation performance of the composites. By reasonably adjusting the content of MBS and silk fiber, the properties of MBS/SF/PLA composites can be optimized, which provides a new idea for the application of environmentally friendly biodegradable materials in electrical insulation and other fields. Future research will deeply analyze the microstructure and interface characteristics of composites and fully understand their performance optimization mechanism.