The invention relates to a self-adaptive adjusting method for laying tension of a prepreg narrow band, and belongs to the technical field of automatic laying forming of composites. According to the method and a device, a prepreg narrow band roll, a supporting structure of the prepreg narrow band roll, a brake, a tension position detector, a tension adjuster, an auxiliary guide roll, an electrical signal processing unit and the like are mainly included. If a pneumatic brake is selected as the brake, an electrical proportion conversion controller needs to be additionally arranged. An adjusting system for the laying tension of the composite prepreg narrow band is suitable for an automatic composite wire laying machine, the response speed is high, independent self-adaptive closed-loop control over the laying tension of the prepreg narrow band can be achieved, modular design can be achieved, dependency on a master control system of the automatic wire laying machine is avoided, the load of the master control system of the automatic wire laying machine is greatly reduced, and the design of the master control system is simplified.