The invention discloses a foot positioning device and method used for ultrasonic bone density measurement. The device comprises a man-machine interaction interface, a signal acquisition module and an ultrasonic bone density instrument. Positioning and measuring software is installed in the man-machine interaction interface, a pressure sensing module is installed on a pedal in a groove of the ultrasonic bone density instrument, the man-machine interaction interface sends an instruction to control the signal acquisition module to acquire signals, foot pressure signals are converted into electric signals through the pressure sensing module and transmitted to the signal acquisition module, the signal acquisition module sends the acquired signals to the positioning and measuring software through the man-machine interaction interface, the positioning and measuring software builds a foot position model according to data uploaded by the signal acquisition module, and the current position of a foot of a user is calculated and analyzed. Correctness and repeatability of foot position placement of the user are guaranteed by judging reasonability and effectiveness of foot position placement in the bone density measuring process, and accuracy and repeatability of bone density measurement are further improved.