The invention relates to a chassis of a strap-on high-pressure gas long pipe transport semi-trailer and belongs to the technical field of lorries. The chassis comprises a frame assembly, a side protection assembly, an axle assembly, a tire assembly and a suspension assembly. The side protection assembly is located at the upper end of the frame assembly, and the axle assembly, the tire assembly and the suspension assembly are installed at the lower end of the frame assembly to form a walking mechanism. The side protection assembly is of a front-and-back split structure. The frame assembly comprises a front frame assembly body and a rear frame assembly body which are fixedly connected with the front end and the rear end of the side protection assembly respectively. The walking mechanism is arranged at the lower end of the rear frame assembly body. The chassis transfers bearing positions to uploaded high-pressure gas bottles through the front frame assembly body and the rear frame assembly body which are in a split type, a frame only achieves a loading function rather than a bearing function, the chassis is lightened, uploading weight can be increased, the volume to weight ratio of the semi-trailer is increased accordingly, and transport efficiency is remarkably improved.