The invention discloses a repairing method and repairing circuit for the capacity of an ex-service lithium ion battery. According to the repairing method, the repaired ex-service lithium ion battery is charged in a periodic small current bidirectional pulse mode, polarization effects generated by the ex-service lithium ion battery in all charging cycles can be eliminated, tiny lithium metal dentrites adhered to an original negative electrode material can be eliminated, and therefore part of the lithium metal dentrites on the negative electrode can be recovered into lithium ions with the activity; and after being fully charged, the ex-service lithium ion battery is discharged in a small constant current mode, after the process is repeatedly conducted for multiple times, the capacity can be recovered to a certain extent, and therefore the ex-service lithium ion battery can achieve higher application value and store more electric energy when being applied to an energy storage system by echelons; and along with development of the new energy vehicle industry, a large quantity of ex-service lithium ion batteries can be generated every year, and by applying the patented technology to the ex-service lithium ion batteries, an important significance can be achieved for development of the new energy industry and the energy storage industry.