The invention provides a method and device for dynamic gas mixing and filling under pressure within a wide range. The method comprises the steps that SF6 gas and sample gas are mixed under the control of a mass flow controller, and the concentration of the sample gas is reduced; the diluted sample gas and the SF6 gas are mixed and diluted under the control of a mass flow controller; the sample gas subjected to secondary dilution and the SF6 gas are mixed and diluted under the control of a mass flow controller; and finally, the mixed gas is injected into a standard gas cylinder. According to the device, an SF6 gas cylinder is connected with the standard gas cylinder through a main gas circuit, and the main gas circuit is sequentially provided with a pressure reducing valve, a first mass flow controller, an electromagnetic valve, a first static mixer, a second mass flow controller, a second static mixer, a third mass flow controller, a third static mixer, a buffer tank, an electromagnetic proportioning valve and a diaphragm press; the SF6 gas cylinder is also connected with the input end of the second static mixer through a fourth mass flow controller and connected with the input end of the third static mixer through a fifth mass flow controller; and sample gas cylinders are all connected with the input end of the first static mixer through a sixth mass flow controller.