In the teaching of bridge engineering, the catenary equation deduction of the main arch circle of arch bridge and the main push towing rope of suspension bridge is one of difficulty. This part of content is explained one by one in different chapter, is less effective, and lack of the comparison between the two catenary equations, student is hard to understand.With the stress characteristic of this two bridge types, the paper analyses the two catenary equations to help the students understand this part of content and improve the students’ ability solving actual problem with mechanics knowledgeof bridge engineering, strengthen learning interest.