A three-dimensional ultrasonic imaging system comprising a vertical stand, a support structure for supporting a patient, a computer, as well as an ultrasound scanner, a space sensor, and a first display connected to the computer respectively, the ultrasound scanner being provided with an ultrasonic probe, wherein the space sensor is configured to detect space information relating to the position and orientation of the ultrasonic probe; wherein the support structure is mounted on an upper part of the vertical stand; the three-dimensional ultrasonic imaging system being characterized by a gravity balance board mounted under the vertical stand and connected to the computer, and a second display connected to the computer; wherein the vertical stand has a U-shaped structure along two sides of which a sliding slot is arranged respectively in a vertical direction; the support structure comprises several supporters which are slideable along the sliding slot, each of the supporters employing a structure whose length is adjustable; the gravity balance board being configured to measure feet pressure distribution data information of the patient, and to send the feet pressure distribution data information to the computer; wherein after processing the feet pressure distribution data information, the computer is adapted to obtain feet position data information and feet gravity point position data information of the patient, and to send the feet pressure distribution data information, the feet position data information, and the feet gravity point position data information to the second display which is configured to display same; wherein the gravity balance board comprises a supporting board mounted on the vertical stand, a measuring board arranged on the supporting board, several pressure sensors mounted above the supporting board and contacting the measuring board, and a data processing unit connected to the pressure sensors; wherein the pressure sensors are configured to collect a pressure signal sensed by the measuring board, and wherein after processing the pressure signal, the data processing unit is adapted to obtain the feet pressure distribution data information, and then to send the feet pressure distribution data information to the computer; and wherein, the measuring board comprises a first foot board and a second foot board around which the several pressure sensors are distributed uniformly. characterized by a gravity balance board mounted under the vertical stand and connected to the computer, and a second display connected to the computer; wherein the vertical stand has a U-shaped structure along two sides of which a sliding slot is arranged respectively in a vertical direction; the support structure comprises several supporters which are slideable along the sliding slot, each of the supporters employing a structure whose length is adjustable; the gravity balance board being configured to measure feet pressure distribution data information of the patient, and to send the feet pressure distribution data information to the computer; wherein after processing the feet pressure distribution data information, the computer is adapted to obtain feet position data information and feet gravity point position data information of the patient, and to send the feet pressure distribution data information, the feet position data information, and the feet gravity point position data information to the second display which is configured to display same; wherein the gravity balance board comprises a supporting board mounted on the vertical stand, a measuring board arranged on the supporting board, several pressure sensors mounted above the supporting board and contacting the measuring board, and a data processing unit connected to the pressure sensors; wherein the pressure sensors are configured to collect a pressure signal sensed by the measuring board, and wherein after processing the pressure signal, the data processing unit is adapted to obtain the feet pressure distribution data information, and then to send the feet pressure distribution data information to the computer; and wherein, the measuring board comprises a first foot board and a second foot board around which the several pressure sensors are distributed uniformly.