The invention discloses a kind of high-viscosity flame-retardant water-based hydraulic fluid, which consists of 90 to 80 percent by weight of water, 10 to 20 percent by weight of hydrophilic and oleophylic dispersing agent, rust-proof agent, tackifier, antiwear agent and defoaming agent. The moving viscosity of the high-viscosity flame-retardant water-based hydraulic fluid can reach 20 to 100 mm<2>/s under the temperature of 30 DEG C, and the defoaming speed and long wearing value of the hydraulic fluid are equivalent to that of No. 32 and No. 46 hydraulic oil; and due to the adoption of the high-viscosity flame-retardant water-based hydraulic fluid, positive effect for reducing the cost and the oil pollution can be realized.