To analyze the turning passing ability of double semi-trailer road train with dolly (B-Train), this paper builds a B-Train model by using TruckSim, and conducts a right-angle turn test and a steady static circular test with a certain steering wheel angle on dry pavement.we analyze the influence of trailer length on the turning channel width, and built the relation model between trailer length variation and turning channel width.The results show that increasing trailer length leads to the increase of the turning channel width of B-Train in two simulations: in the right angle turn test, the change of turning channel width is almost the same when the length of each trailer increases independently;in the steady static circular test,the turning channel width is larger when the length of the second trailer is increased independently than that when the length of the first trailer is increased independently.