The invention discloses an internal partition plate of a steel plate house for buildings. The internal partition plate comprises a main body plate, extension plates are slidably mounted at the left end and the right end of the main body plate, lifting assemblies are arranged in inner cavities of the extension plates, extrusion fixing assemblies are arranged at the upper ends of the lifting assemblies, a partition plate door is extruded at the outer end of the extension plate on one side, a supporting base is inserted into the lower end of the main body plate, the lower ends of the extension plates and the lower end of the partition plate door. According to the internal partition plate, the main plate body is matched with the two extension plates, the overall transverse area after the main plate body and the two extension plates are spliced can be enlarged, so that the main plate body and the extension plates are suitable for being used in steel plate houses with different lengths or widths, meanwhile, the main plate body, the extension plates and the partition plate door can be detached, so that disassembly and handling of the steel plate house after use are facilitated; after the main plate body, the extension plates and the partition plate door are assembled, the main plate body, the extension plates and the partition plate door are fixed in the steel plate house through the extrusion fixing assemblies and the supporting base, so that the mounting position of the main plate body, the extension plates and the partition plate door can be adjusted at any time in the steel plate house, and the requirement of people for space is met.