The invention provides an auxiliary construction method for demolishing a reinforced concrete pile without removing a building structure. The method comprises the following steps that 1), concrete wrapped at the two ends of the reinforced concrete pile is demolished, and rebars at the two ends of the reinforced concrete pile are exposed; 2), an electrolyte solution is injected into the bottom endof the reinforced concrete pile through punching; 3), an electrode is placed in the electrolyte solution, the electrode is enabled to communicate with a negative electrode of a power supply, and meanwhile, the rebar at the top end of the reinforced concrete pile is enabled to communicate with a positive electrode of the power supply, so that rebars in the reinforced concrete pile are electrolytically corroded; and 4), the reinforced concrete pile after electrolytic corrosion is cut. According to the method, corrosion of the rebars in the reinforced concrete pile is accelerated by utilizing anelectrolysis principle, after the rebars are corroded, expansion stress generated by corrosion enables the concrete to crack, cracking of the concrete also reversely accelerates the corrosion of the rebars in the reinforced concrete pile, and the bearing capacity of the reinforced concrete pile is greatly weakened, so that cutting is convenient, and the construction risk and the cost are reduced.