The concrete arch bridge is a natural and appropriate structural solution, aesthetically pleasing and easily integrated into the environment, especially in mountainous and island areas. However, construction difficulty and cost will increase with heavy self-weight when the span enlarges. A potential solution is to use a composite box arch ring with steel web-concrete flange. Taking Wanzhou Yangtze River Bridge (the longest concrete arch bridge in the world with a main span of 420 m) as a prototype, trial designs of a composite box arch with steel webs (including corrugated steel webs and plain steel webs) and concrete flanges were carried out. Comparison of quantities and structural behaviors of the prototype concrete arch with the two trial designed composite arch was presented. It is shown that the self-weight of the composite arch can reduce about 28% and the structures can meet the design requirements, therefore it is possible to use the two composite arches in long span arch bridges.