Provided is a blanket installation method, which includes a transporting step of transporting a blanket unit (1), in which the blanket (2) and a transport jig (3) are coupled in one body, between an inner tank (60) and an outer tank in a double shell tank, in a suspended condition, and a mounting step of mounting the blanket unit on a shell plate of the inner tank. According to the method, in the event of installing work of the blanket, the improvement in work efficiency and safety can be achieved.