The present invention provides a method and apparatus for fast 3D ultrasound imaging. The method comprises data acquisition, desired data selection, data smoothing, table construction, ray casting, table look-up, ray synthesis and final result output. The apparatus comprises an acquisition module, a table look-up module, a synthesis module and an output module. The present invention can avoid a huge amount of unnecessary reconstruction calculations by smoothing preprocessing and constructing the reconstruction table and the gradient table as well as transforming coordinates of the points where necessary. The present invention has greater practical applicability, because the existing imaging technology demands that the radius for rotating the probe be identical to the radius of the probe.