The invention relates to a method for prolonging the service life of an A-plane sapphire window polishing fluid. The method comprises the following processes: 1), during chemical and mechanical polishing of an A-plane sapphire, taking the A-plane sapphire window polishing fluid, and measuring the potential by using a Zeta potential analyzer to monitor the change condition of the Zeta potential ofthe A-plane sapphire window polishing fluid; 2), when the absolute value of the Zeta potential of the A-plane sapphire window polishing fluid is monitored to be not higher than 18 mv, directly addinga non-ionic surfactant into the A-plane sapphire window polishing fluid in use, when the absolute value of the Zeta potential of the A-plane sapphire window polishing fluid is not lower than 25.0 mv,stopping adding, then monitoring the Zeta potential once every 0.5-1.5 hours, and repeating the process, wherein the non-ionic surfactant is one or a mixture of several of fatty acid methyl ester ethoxylate, dodecyl polyethylene glycol carboxylate and fatty alcohol polyoxyethylene ether which can increase the Zeta potential of the polishing fluid and do not adversely react with the polishing fluidafter addition.