Most existing cutting-off machines on production lines for continuously-formed materials such as steel pipes and profile steel are single-trolley synchronous and fixed-length cutting-off machines, only one trolley provided with a cutting tool is available, the stroke of the trolley is small, the material cutting time of the cutting tool is short, and the cutting tool is not suitable for cutting short-length products and not suitable for a high-speed production line either. In order to overcome the defects of the prior art, the invention provides a novel method for synchronous and fixed-length cutting-off of continuously-formed materials through multiple trolleys connected in series, in particular to a multi-trolley series-connection synchronous and fixed-length cutting-off machine. The multi-trolley series-connection synchronous and fixed-length cutting-off machine is provided with two or more trolleys provided with cutting tools. The trolleys are installed on a rail parallel to the materials in a series connection mode and driven by corresponding driving devices to walk back and forth according to a set procedure, and the cutting tools on the trolleys cut off the materials according to a set length under the condition that the material speeds are synchronous. The cutting-off machine can be adapted to production lines at high speeds, the allowable minimum fixed length is small, the service life of the cutting tools is long, the quality of notches is good, and the number of times of halts for cutting tool replacement is small.