A cooperative adaptive cruise control algorithm is designed for commercial semi-trailers' platoon based on sliding mode control theory. Two inter-vehicle communication modes, the communication between adjacent vehicles and that between leading vehicle and following vehicles, are adopted for longitudinal motion control of commercial semi-trailers' platoon. Then, the performance of the designed controller is illustrated and compared with computer simulations using MATLAB and TruckSim software. Simulation results showthat, compared with the communication between adjacent vehicles, the communication between leading vehicle and following vehicles can reduce the response time and the inter-vehicle space effectively. Besides, it can increase the stability and safety of semi-trailers' platoon, improving the traffic capacity.