The invention discloses an adjustable track semitrailer, comprising a frame assembly, a power gooseneck, a track adjusting device and a steering system; the frame assembly includes a left frame assembly and a right frame assembly arranged in bilateral symmetry and both arranged in high-front low-rear structure; both one end of a front jib assembly of the track adjusting device and one end of a rear jib assembly are connected to the frame assembly, the other ends are connected with a supporting butt joint on the power gooseneck, and two ends of a rear adjusting cylinder are connected with the left frame assembly and the right frame assembly respectively; a steering porous plate of the steering system is fixed to a suspension assembly, rotary discs are connected with the frame assembly through pins, and two ends of a steering transverse tension rod are connected with the two bilaterally symmetric sets of rotary discs respectively. The adjustable track semitrailer according to the technical scheme can be bilaterally adjusted according to different goods widths; the ability of the adjustable track semitrailer to transport super-wide and super-high goods is improved at the premise of transportation of super-long goods, steering radius is decreased, steering efficiency is improved, and tire wear is relieved accordingly.