An inverter, a sealing air duct, and a heat dissipation system are disclosed. The inverter includes: an enclosure having a first cavity and a second cavity that are isolated from each other and sealed; a magnetic conversion circuit including magnetic elements that is arranged in the first cavity; a power conversion circuit including power tubes that is arranged in the second cavity; a heatsink arranged at the bottom of the enclosure and located outside the first cavity and the second cavity; a sealing air duct arranged outside the second cavity, where the columnar pipeline is sealed at two ends, the bottom surface is formed by a side wall of the second cavity or a substrate of the heatsink, and the bottom surface includes an air inlet and an air outlet to communicate with the second cavity and the at least one columnar pipeline.