The invention discloses a device and method for measuring a stainless steel sub-microamp metastable point corrosion transient current under alternating load and belongs to the technical field of stainless steel local corrosion mechanism research under mechanical-chemical interaction. Through selection of a reasonable solution environment and a work electrode area, a background passivation current is reduced to a sub-microamp level so that sub-microamp transient current resolution is realized. An electrochemical workstation has a nanoamp-level current monitoring capability. Through use of floating of the electrochemical workstation and combination with an insulation sheet, interference on real current signal measurement in cyclic loading is effectively eliminated. The device and method research necessary conditions of cyclic loading parameter, polarized potential and environmental factor change-caused influence on stainless steel metastable point corrosion behavior. The method realizes monitoring of a metastable point corrosion transient current signal under reasonable combination of different inactive materials, an environment spectrum and a load spectrum.