The invention discloses an expandable graphite preparation device and an electrochemical intercalation method thereof, and belongs to the field of crystalline flake graphite electrochemical intercalation. The device comprises a wrapping pocket, an electrode, a direct current voltage-stabilizing and current-stabilizing power supply, a quick plug connector, a cross beam, an electrolytic cell, a circulating cooling device, a thermocouple, a first servo motor, a support frame and a second servo motor. The method comprises the steps of preparation of a chemical electrolyte, bag filling of natural crystalline flake graphite, electrode assembly and electrochemical intercalation preparation, electrochemical intercalation treatment, and treatment of an intercalation compound. According to the method, natural crystalline flake graphite can be efficiently intercalated to prepare expandable graphite, the prepared expandable graphite does not generate smoke and irritant gas in the microwave expansion and high-temperature expansion processes, and the expansion ratio can reach 200-300 mg / L. The problems of production safety and environmental pollution related to expandable graphite preparation can be solved from the source, large-scale preparation and engineering application of expandable graphite can be actively promoted, and the market application prospect is wide.