Abstract: A negative-pressure balance system for a gearbox of a centrifugal compressor includes the gearbox, a hermetically-sealed low-level oil collecting tank and a U-shaped negative-pressure balance pipe. The gearbox is connected to a respirator, and the back pressure of the respirator is a local ambient atmospheric pressure. The bottom of the gearbox and the low-level oil collecting tank are connected by an oil conduit. An oil demister communicated with the low-level oil collecting tank is mounted at the top of the low-level oil collecting tank. The oil demister at least includes a ventilation device. The respirator is communicated with a front-end lubricating point in the gearbox. One end of the U-shaped negative-pressure balance pipe is communicated with the respirator, and the other end of the U-shaped negative-pressure balance pipe is communicated with a rear-end lubricating point in the gearbox.