The invention discloses a tinplating method and a tinplating device of a photovoltaic welding belt. A copper belt is released by a discharging end of a two-shaft winding system to a single straight wire, the single straight wire is sealed by a sealing flange assembly with circular exterior and square inside, then the single straight wire enters an auxiliary vacuum cavity, and then after being sealed by a sealing assembly, the single straight wire enters a plasma processing cavity; after the treatment is completed, the single straight wire enters the auxiliary vacuum cavity after being sealed by the sealing assembly and directly enters a hot tinplating device after being unsealed by the sealing assembly, and a photovoltaic welding belt can be produced and formed after the tinplating is completed. By utilizing the tinplating device and the tinplating device of the photovoltaic welding belt, continuity in treatment and tinplating can be realized, the process efficiency can be improved, the production cost is reduced, and the good quality consistency can be maintained; moreover, high pollution raw materials such as soldering flux can be avoided, and energy-saving and environment-protecting effects can be realized.