Pressure-controlled drainage gas production method and system for coal-bed gas well

The invention discloses a pressure-controlled drainage gas production method and system for a coal-bed gas well. The pressure-controlled drainage gas production method comprises the steps that drainage is conducted through the first daily drainage amount, wherein the first daily drainage amount meets the eliminating demand for production interference objects in a coal bed; and a pressure-supplementing medium is injected while drainage is conducted, and the downhole flow pressure daily drop amount is maintained as a first differential pressure value so as to avoid retracting and closing of pores and cracks in the coal bed. According to the pressure-controlled drainage gas production method for the coal-bed gas well, the drainage speed at the drainage state can be conveniently determined, the eliminating demands for drilling and completion fluids, pulverized coal and slack coal in the coal bed can be met, and meanwhile, retracting and closing of the pores and the cracks in the coal bed can also be avoided; and compared with the prior art, the pressure-controlled drainage gas production method is simple in process, the production efficiency of the coal-bed gas well can be greatly improved, and quite high practical value and popularization value are achieved.