The invention discloses an integral multi-stack system of fuel cell. The system includes at least one pair of fuel cell stacks, a manifolding functional frame, and an attaching device for securely installing each pair of fuel cell stacks to the manifolding functional frame. Each fuel cell stack has a pair of end plates and six openings including a fuel inlet, an oxidant inlet, a cooling agent inlet, a fuel outlet, an oxidant outlet, and cooling agent outlet all formed on one end plate thereof. When the fuel cell stacks are securely installed onto the manifolding functional frame, each opening thereof is air commnicateable to a sub-passage defined in the body without being communicated with one another and respectively communicated to a plurality of main passages defined in the body, making the main passages and the sub-passages be able to be used to supply and/or discharge gas or liquid being used by all the fuel cell stacks integrated.