The invention discloses a converter station valve cooling main pump online maintenance water replenishing work vehicle, and relates to a special-purpose water replenishing device specially applied to power-failure-free maintenance of a main pump of a converter station converter valve cooling system. The work vehicle is characterized by comprising a mobile platform vehicle, a water storage tank fixed on the mobile platform vehicle, and a self-loop softening branch, a self-absorption water injection branch and an external connection water replenishing branch which are respectively connected with the water storage tank. The converter station valve cooling main pump online maintenance water replenishing work vehicle has the following advantages: work vehicle is convenient, can be moved and can be manually dragged to any work sites for operation; the operation is finished through a simple control circuit, and the operation is simple; and the apparatus provided by the invention can independently finish softening and replenishing operation of purified water and is free from wrong operation risks.