Provided is a re-heater flue intermediate separation plate sealing device and an installation method. In the prior art, a temperature adjustment baffle used for separating the interior of a hearth and an intermediate partition structure between headers are not provided. Among millions of tower-type boilers, the original structure is not applicable and cannot solve the seal and expansion problems of a re-heater flue intermediate separation plate. The re-heater flue intermediate separation plate sealing device comprises an intermediate hydrophobic plate (1), wherein the intermediate hydrophobic plate is respectively connected with a first intermediate separation plate(4), a second intermediate separation plate(5) and a third intermediate separation plate(6), and the first intermediate separation plate and the second intermediate separation plate are sealed by the third intermediate separation plate and the fourth intermediate separation plate(7) respectively. The re-heater flue intermediate separation plate sealing device and the installation method are applied to a boiler of which the smoke is in a circular air flue.