The invention discloses an activation and regeneration method of a deactivated catalyst in a process of synthesizing dimethyl oxalate by CO. The activation and regeneration method mainly comprises the following steps: washing the deactivated catalyst with alkali at high temperature and under high pressure and removing organic matters attached on the surface of the catalyst; immersing with a pore-expanding agent solution and roasting at 400 DEG C to 700 DEG C to remove deposited carbon attached on the surface of the catalyst and dredge a blocked pore channel of the catalyst; purging with mixed gas of nitrogen gas and hydrogen chloride to disperse an active Pd material which grow large by agglomeration again; immersing with alkali liquid and fixing the Pd material, which is dispersed again, on a carrier; finally, reducing with the catalyst through two steps including a wet process and a dry process, so as to reduce palladium oxide into palladium. The deactivated catalyst is subjected to activation treatment by the method and the agglomerated and sintered active Pd material is effectively dispersed; the activity of the catalyst can be recovered to be about 96 percent of original activity. The method provided by the invention is simple in process, easy to operate and low in cost, and circulating utilization of a noble metal catalyst is realized.