The invention relates to a three-dimensional reconstruction method for a two-dimensional ultrasonic image. The method comprises the following steps of: acquiring data of a two-dimensional image in a mechanically-driven scanning mode; judging a scanning type, and processing the data of the two-dimensional image by adopting a sector scanning/rotary scanning processing algorithm to generate a regular data field if the scanning is sector scanning or rotary scanning; and displaying a three-dimensional image by utilizing the regular data field through a ray casting algorithm. The sector scanning processing algorithm comprises the processing steps of: extracting interesting areas, namely rejecting unwanted data information; calculating the size of the regular data field to obtain the length, width and height of the regular data field; improving coordinate conversion and an interpolation algorithm to obtain a grey value of a current pixel; and performing filtering processing. In the method, the three-dimensional reconstruction is performed on the data of the two-dimensional ultrasonic image which are acquired in different scanning modes; and the method has the advantages of clear reconstructed images, strong sense of reality, high imaging speed and the like.