The invention discloses a new process for comprehensively recovering scandium in gas ash by using waste acid. The waste acid for scandium-contained gas ash is filtered after normal-pressure leaching I; solution obtained by filtering is neutralized by the scandium-contained gas ash after being reduced by reducing agent; obtained neutralized slag is leached at normal pressure by the waste acid; and extraction, back extraction, and precipitation by adopting oxalic acid are performed on the filtrate obtained by leaching to obtain scandium oxalate. The new process treats the gas ash through the waste acid, that is, wastes are used, high-value elements are recovered, and the economic value is high; and meanwhile, the process conditions are easy to realize, the scandium is enriched and recovered, metal such as zinc and iron in the gas ash is recovered, and the comprehensive resource utilization of the gas ash in a blast furnace is realized. The new process is simple in treatment method, obvious in effect and high in popularization significance.