This paper aims to propose a flexible and simple design method for bottom forming structure of paper cartons with tuck top snap-lock bottom, to solve the non-standard problems existing in structural design of various paper cartons with tuck top snap-lock bottom in actual production. Starting from the analysis on strengths and weaknesses of various kinds of paper cartons with tuck top snap-lock bottom in the market, this paper classified different structures of paper cartons with tuck top snap-lock bottom, analyzed the tuck top snap-lock bottom structures of different types of paper cartons, and put forward the most reasonable key points for the structure design of tuck top snap-lock bottom. Compared with traditional design methods, the design method presented in the paper can improve the working efficiency by 0.6-1 time. Moreover, this method was more effective for the non-cubic paper box. In this paper, the midline theory is put forward, and the tolerable interval length of the midline is given under the condition that the bottom of the packaging box is firm and free from penetration. It is more convenient. It saves time and improves production efficiency than applying existing formulas by rote.