The invention discloses a core switching and sealing system of a valve and belongs to the field of core sealing. The system comprises a valve rod with an annular groove and a plastic gasket in the same volume as the annular groove, wherein the annular groove has a large cavity and a small opening and is used for completely clamping the plastic gasket in the annular groove; and the thickness of the plastic gasket and the depth of the annular groove are equal, and the plastic gasket is used together with the annular groove to complete the sealing of the valve. The annular groove is designed with the shape with the large cavity and the small opening for completely clamping the plastic gasket in the annular groove, the volume of the annular groove is equal to that of the plastic gasket and the thickness of the plastic gasket is equal to the depth of the annular groove, so that the plastic material has no space for cold flows and the valve sealing is reliable even in alternating temperature environments are guaranteed effectively; and at the same time, the plastic gasket cannot separate from the valve rode due to the clamping action of the annular groove.