The hydraulic modular trailer ( full or semi traction) is mainly compsed by the structures of flat grid main box beam vehicle frame, hydraulic suspension, three point support, hydraulic full wheel tractive turning or power assisted steering, double-pipe hydraulic circulating, etc. It has the advantages such as adjustable cargo platform height, even axle load, small turning radius, convenient go astern, etc. When running on upramp or downramp, as well as slope, the vehicle body can adjusted to the level position to ensure the stability of cargos. The hydraulic combined semi trailer is the product deriving from the full trailer. Both of them are identical on the sturcture and have the functions of longitudinal and vertical splice.