The invention relates to an assembly for providing constant oil suction pressure for a hydraulic pump. A hydraulic pump is a vehicle-mounted hydraulic system hydraulic pump, wherein the assembly comprises a liquid medium storage device (2), a liquid medium input pipeline and a liquid medium output pipelines, wherein the liquid medium input pipeline and the liquid medium output pipelines connectedwith the storage device (2), the assembly is characterized in that the number of the medium input pipeline is 1, and the number of the medium output pipelines is 2; and the storage device (2) is a sealed storage device (2) of which the longitudinal section is in a convex shape and is internally provided with a longitudinal piston (3). According to the technical scheme, the structure is simple, theuse is convenient, and the assembly is capable of resisting vibration and impact.