The invention belongs to the technical field of secondary valuable metal comprehensive recycling, and particularly relates to a method for recycling a waste circuit board by low-temperature molten mixed alkali treatment under ultrasonic action. The method mainly comprises the steps of waste circuit board crushing treatment, low-temperature molten mixed alkali leaching under ultrasonic action, organic resin pyrolysis, emission gas purification treatment, glass fiber and molten alkali chemical reaction under ultrasonic action, alkali melt and solid metal residue separation, alkali melt centrifugal separation and recycling, precious metal enrichment, valuable metal separation and the like. Compared with a traditional waste circuit board metal recycling process, the method has the characteristics of high separation rate of metal and non-metal of a waste circuit board, harmless treatment of bromine elements in a brominated flame retardant, no harmful gas emission, high recycling rate of valuable metal, lower operation temperature and the like, and high-additional-value recycling of metal resources in the waste circuit board is realized under the conditions of cleaning, high efficiency,low energy consumption, short flow and the like.