The utility model discloses a sliding door adjusting device. The sliding door adjusting device comprises a cavity shell. A transverse adjusting mechanism and an adjusting wheel connected with the transverse adjusting mechanism are arranged in the shell. The transverse adjusting mechanism comprises a transverse gear, a taper tooth screw, a threaded sliding block, a bearing sliding block and springs, wherein the transverse gear, the taper tooth screw, the threaded sliding block, the bearing sliding block and the springs are in linkage with one another. The transverse gear is arranged at the upper end of the taper tooth screw. The upper portion of the taper tooth screw is connected with the transverse gear in a clamped mode. The lower portion of the taper tooth screw is connected with the upper portion of the threaded sliding block. The springs are arranged on the two sides of the threaded sliding block. The lower portions of the springs are fixed to the upper end face of the threaded sliding block. A traditional vertical adjusting method is changed, the height of a sliding door can be adjusted by adjusting the transverse gear, the adjustment is fast and convenient, the structure is simple, and conversion from vertical adjustment to transverse adjustment is successfully achieved; moreover, the sliding door adjusting device is low in manufacturing cost, convenient to use, and capable of effectively preventing the adjusting wheel from running off a rail, thereby being safer to use.