The invention discloses a scumming mechanism of a scum scraping and sucking machine. A baffle is pivoted on an end plate of a scumming plate via a pivot, a spring is arranged between an inner side of the baffle and the end plate, and an outer side at the front end of the baffle is abutted against a side of a harrow plate by the aid of elasticity of the spring. Two H-shaped suspension arms are utilized to hang a scum scraping harrow, so that rigidity and stability of the scum scraping harrow are remarkably improved, and deflection of the working scum scraping harrow can be avoided. The stainless steel baffle side is tightly abutted against the side of the harrow plate by the aid of the elasticity of the spring to keep a sealing performance, when scum passes a scum discharging hopper, the elasticity of the spring is restrained so that the baffle can give way to the scum to pass through smoothly, a defect that a rubber part is prone to abrade and needs to be replaced frequently is overcome, scum leakage caused by an abraded sealing part is avoided, and accordingly, scum scraping effect is remarkably improved.