Screw-type oil-free dry mechanical vacuum pump is the use of gear synchronous reverse rotation of the intermeshing and non-contact left and right screws for high-speed rotation, the use of the pump housing and intermeshing spiral spiral groove separated into multiple spaces to form Multiple stages, the gas is transported in equal slots (cylindrical pitch), but without compression, only the helical structure at the very end of the screw has a compressive effect on the gas. Screw pressure gradient between the various levels can be formed to disperse pressure and improve the compression ratio. The gap and pump speed of each department have a great influence on the performance of the pump. Screw in the design of the various parts of the gap, we must consider the expansion, processing and assembly accuracy and working environment (such as the removal of dust-containing gas, etc.). The pump and Roots vacuum pump without exhaust valve. Pump is a vertical structure, the intake port above, the exhaust port in the middle, the lower part of the motor and lubricating oil pool. Screw rotor was hollow, cantilever support structure. Synchronous drive gear is located below the bearing support. The variable frequency motor is connected with the active rotor through the coupling. The pump gas path is shorter, and the vertical structure of the exclusion of dust-containing gas is more favorable. Pump housing with water cooling, pump maintenance is also convenient. This type of pump, if used with a suitable simpler screw profile, is simple to manufacture, guarantees high machining accuracy and is easily balanced.