The invention discloses a kelp preprocessing device. The kelp preprocessing device comprises a conveying motor, parallel conveying chains and a plurality of support racks. The conveying chains are driven by the conveying motor to run a driving chain wheel and a driven chain wheel and circularly pass through a feeding station, a boiling tank, a cooling tank, a separator and a discharging station. The kelp preprocessing device is characterized in that hanging rods with clamping fixtures are arranged at intervals between the conveying chains; the support rack of the feeding station is provided with a feeding anti-spinning plate, which is provided with an feeding fixture opening slider for opening the clamping fixtures; the separator is composed of cutting racks gradually elevated in station, a separating motor, a cutter shaft and a round cutting blade; the support rack of the discharging station is provided with a discharging anti-spinning plate, which is provided with a discharging fixture opening slider for opening the clamping fixtures. The kelp preprocessing device can achieve mechanization and automation of boiling, cooling, separating and discharging of kelp and is low in labor intensity of workers, high in production efficiency, even in kelp boiling and cutting and uniform in specification of separated positions of kelp.