The invention discloses an auxiliary system of an ultrasonic scanning device. The auxiliary system comprises an ultrasonic probe, a robot, a control module and a placement module. A mechanical arm of the robot is used for fixing and controlling the ultrasonic probe. The placement module comprises a weight sensing unit and a touch sensing unit. The weight sensing unit and the touch sensing unit measure and upload data to the control module, and the control module draws a profile image of a target to be scanned on the basis of the uploaded data, matches the profile image with an internal template image, outputs the internal template image, controls the robot to perform ultrasonic scanning on the basis of the internal template image and receives scanned data. A placement platform which can measure the weight and perform touch sensing is built, position information of the target to be scanned is obtained through processing of gravity and touch data, an optical image is replaced for performing positioning on an object to be scanned, a region to be scanned can be rapidly determined, the robot can replace manpower for controlling the ultrasonic probe, and the scanning efficiency can be improved.