The laboratory studies on the mechanical properties of the GFRP beams with two different sections are carried out. Their mechanical behavior and the failure features are described and analyzed. The test results indicate that the stability of the GFRP middle beam and the local strength at the joint between the web and the flange are the main factors in the design of the composite middle beams. Based on the test results, a new-style GFRP middle beam with- I-section and double webs is proposed and designed. Loading test shows that the composite material with I-section and double webs can satisfy the requirements for the globe and local stabilities, and simultaneously the material strengths of the middle beam can also be fully utilized. Maybe the proposed new-style beam is the best section type for the middle beam. Also, local strengthening should be adopted in the middle beam-bolt joint.