The invention relates to a height adjusting device of medical diagnostic equipment, in particular to a lifting structure of a scanning bed. The lifting structure of a scanning bed comprises a bed board component, a base and a plane link mechanism hinged between the bed board component and the base, wherein a driving device installed on the base is arranged between the bed board component and the base, the other end of the driving device is connected with an adjusting device which adjusts the acting force arm thereof, and the driving device is connected with the plane link mechanism via the adjusting device. The invention jointly acts by a first linkage, a second linkage and the driving device to change the space between a seventh spindle and a second spindle so as to dynamically adjust the force arm size of the acting force of the driving device to ensure that the force arm is suitable for loading moment changing needs when the bed plate part is at different heights; in the process oflifting movement, acting force needing to be provided by the driving device has smaller fluctuation and stable movement by adjusting the acting force arm of the driving device.