The invention discloses a preparation method of active carbon capable of selectively adsorbing radon gas, and gas purification equipment. The method comprises: S1, pre-treating active carbon; S2, carrying out ultrasonic pore forming on the active carbon; and S3, carrying out microwave irradiation in an N2 or H2 atmosphere. According to the invention, commercially available active carbon is simplymodified through ultrasonic pore forming, microwave irradiation under N2 or H2 conditions and the like, so that the specific surface area of the active carbon is about 850 m<2>/g, the volume of the micropores with a pore size of 0.5-0.8 nm is increased, the surface oxygen content is reduced, the selective adsorption capacity of the active carbon to radon gas is improved, the modification method issimple, and the cost is low.