A method for three-dimensional ultrasonic imaging conducting a first group of line scans on a scanning object at a first group of scanning positions receiving echo signals from the first group of line scans, and acquiring a first group of scanning line data carrying out a second group of line scans on the scanning object at a second group of scanning positions receiving echo signals from the second group of line scans and acquiring a second group of scanning line data and acquiring a three-dimensional image of the scanning object according to scanning data comprising the first group of scanning line data and the second group of scanning line data the scanning positions in the second group of scanning positions are shifted by a first distance along a direction parallel with a frame scanning direction relative to the scanning position in the first group of scanning positions corresponding to the scanning position, allowing an increase of joint line space without changing the independent line space, thus the imaging quality is improved without reducing the three-dimensional imaging speed.
