The invention discloses a working fluid system applicable to water-base drilling fluid filter cake removal before well cementing. The working fluid system is composed of the following components in percentage by mass: 0.5-1.5% of solid-phase denudation main agent, 0.1-1% of solid-phase denudation aid, 0.15-0.5% of viscosity breaker, 0.5-1.5% of surfactant, 1-3% of clay stabilizer and the balance of water. The pH value of the solution is regulated to 12-14 by NaOH or KOH. The solid-phase denudation main agent is composed of any one or mixture of ethylenediamine tetraacetic acid, disodium edetate, diethyltriamine pentaacetic acid and pentasodium amino trimethylene phosphonate; and the solid-phase denudation aid is composed of any one or mixture of sodium gluconate, oxalic acid and potassium sodium tartrate. By combining the characteristics of well cementing operation, the working fluid system can shorten the construction time, has higher reaction speed, achieves the goals of removing the filter cake and enhancing the cementing strength of the well-cementing interface, and thus, has broad market prospects.