The work aims to reduce the logistics cost to solve the contradiction between the increasing demand for express package and the waste of social resources and the increase of logistics cost. Firstly, with the international standardized module size as the basis, the module segmentation method was used to design the box size and the design size was preliminarily determined based on the statistics of the distribution of the packaging box size of the e-commerce logistics. Then, based on the modular design and green design, a foldable environmentally friendly packaging box scheme was designed with the degradable material polypropylene, which could not only facilitate folding and recycling, but also change the box size through the modular setting to meet the packaging requirements of commodities with different specifications. Moreover, the fourth strength theory and finite element analysis were used to conduct the mechanical analysis for the verification of its reliability. The box body could realize modularized length adjustment in the length direction. When the box body was 260 mm×180 mm in length and width, 180 mm in height, 5 mm in wall thickness and 5 mm in radius of rounded corners, the overall performance was the best. Under the working conditions of static stacking and transportation acceleration and deceleration, the maximum stress of the box body was less than the compressive yield strength of polypropylene, and the size design was reliable. Featured by good storage performance, recyclability, environmental protection, moisture resistance and flexibility, the foldable environmentally friendly express package has good mechanical properties to ensure the reliability of the use and effectively solve the problems such as non-recyclable express package, excessive commodity packaging and poor safety performance and compressive property.