The invention provides a grid voltage bootstrapping switch circuit based on a NMOS tube. The grid voltage bootstrapping switch circuit comprises a NMOS tube MN1 for sampling, a voltage bootstrapping circuit BOOST, a sampling switch substrate coupling capacitor C1, and a sampling switch MN1 substrate discharging switch MN8; a coupling capacitor C1 is added between the grid and the substrate of the sampling NMOS tube NM1 and the substrate; a discharging switch MN8 is added between the substrate of the sampling switch and the ground; when the input signal VIN is changed, the discharging switch NM8 is disconnected if the sampling maintaining circuit is in the sampling state; through the bootstrapping effect produced by the bootstrapping circuit module BOOST, when the input signal VIN is changed, the discharging circuit NM8 is conducted, and the substrate of the sampling switch NM1 is pulled down to the ground if the sampling maintaining circuit is in the maintaining state; and meanwhile, the grid voltage of the sampling switch NM1 is pulled down to the ground, thereby disconnecting the sampling switch. By using the sampling maintaining switch and the auxiliary circuit thereof provided by the invention, the linearity is obviously improved in comparison with the traditional structure.