The invention relates to an ultrasonic in-plane puncture positioning device. The ultrasonic in-plane puncture positioning device comprises a telescopic arm, the fixed end of the telescopic arm is provided with a clamp, an axial center line of the clamp coincides with a central axis of an ultrasonic probe, and a transverse axis of the telescopic arm is perpendicular to the central axis; the telescopic end of the telescopic arm is provided with a rotating mechanism, the rotating mechanism is provided with a positioning piece, and the rotating mechanism drives an axis of the positioning piece torotate in a plane determined by the transverse axis and the central axis; a micro-calculator is arranged, an ultrasonic machine measures the vertical distance between an intersection point of the central axis and the skin and a puncture endpoint, the micro-calculator calculates the rotation angle of the rotating mechanism according to input data about the vertical distance and data about the horizontal distance between the intersection point and a puncture starting point, and the rotating mechanism drives the positioning piece to coincide with a straight line determined by the puncture starting point and the puncture endpoint. According to the ultrasonic in-plane puncture positioning device, through the telescopic arm, the rotating mechanism, the micro-calculator and the like, rotation ofthe positioning piece for positioning a puncture needle can be achieved, and thus the puncture angle of the puncture needle is precisely positioned.