The work aims to study the relationship between the express box handle, namely the latch structure and the average weight it can bear, so as to facilitate the design and selection of handle size. Through the knowledge of mechanics and ergonomics, the factors affecting the structural performance of the latch structure designed in the express box were analyzed and the strength test schemes for such a latch structure were formulated. According to the test data processing and analysis results, the handle width a could be calculated by the formula generated by MATLAB. When the handle width a/lock wing width b was 0.5-0.8, the bearable weight was 15.33-17.40 kg. When the lock wing length was 20-60 mm, the bearable weight is 3.76-18.26 kg. When the plate margin d was 6-22 mm, the bearable weight was 3.05-5.21 kg. Based on the test data and results, the design steps of latch size are drawn up, which is convenient for the reference of relevant practitioners in the industry.