The invention relates to a positioning ultrathin slice method for a pathologic cell infected with a virus. The method comprises the following steps: (1) with a chamber slide as an embedding die and cells infected with a virus as a model, carrying out in-situ embedding on the cells by using a resin when a lesion occurs in the cells; (2) directly exposing a target cell through trimming or drilling out the target cell and then exposing the target cell through trimming; (3) preparing an ultrathin slice for the target cell; and (4) observing the ultrathin slice of the target cell by using a transmission electron microscope.