Provided is a DC voltage generator capable of automatically converting a polarity. The DC voltage generator has a simple structure and high reliability, is capable of rapidly converting a polarity and comprises a silicon cylinder pillar, a plurality of silicon stack units, a plurality of paired electrodes and a transmission mechanism. The silicon cylinder pillar comprises an inner cylinder and an outer cylinder; the transmission mechanism comprises a pneumatic motor, a speed reducer, a driving shaft, a driven shaft, an active gear and a driven gear, wherein the driven shaft is arranged in the inner cylinder, and the silicon stack units uniformly sleeve the driven shaft; the driving shaft is arranged in the outer cylinder and on the outer side of the inner cylinder. The DC voltage generator utilizes a cylinder transmission mechanism to drive the polarity conversion of the silicon cylinder pillar, wherein the silicon cylinder pillar is composed of a plurality of silicon cylinder units in vertical concatenation, is a single pillar structure, and has reliable pneumatic mechanical transmission and two side ball type electrode contact mode; the electrical contact is reliable and connection is firm. The DC voltage generator has stable performance and is simple to maintain.