The invention discloses a cast-in-situ construction method of beam flange plates of acoustic barriers through movable mold base vehicles, and relates to the technical field of bridge construction. The cast-in-situ construction method comprises the specific construction technological processes of preparing for construction; assembling the mold base vehicles; enabling the mold base vehicles to run to proper positions, and inspecting equipment; enabling templates to drop off to proper positions; enabling finish rolling screw-thread steel to be mounted; binding reinforcing bars, and placing embedded parts; mounting hanging molds and explorators; casting concrete; disassembling molds; lifting bottom molds and shifting to another site. According to the construction method disclosed by the invention, the problem that the cast-in-situ construction of flange plates of a high pier is difficult is solved; besides, the construction method is safe and reliable, and is simple and convenient to apply.