The present disclosure provides a quantitative tank bottom sludge valve. The extension and retraction of a cylinder drives a lower valve body, a valve rod, an upper valve body and respective accessories to move up and down, and sludge at the bottom of a water tank that is deposited to the upper part of an upper valve plate and the lower part of an upper valve body gasket is discharged quantitatively, thereby saving water and avoiding blockage; moreover, the quantitative tank bottom sludge valve has simple components in structure, and it is low in processing and assembly precision requirements, low cost, convenient to install and maintain, and suitable for mass production and use.