1. A method of three-dimensional magnetic resonance imaging, using a sequence controller to execute the steps comprising: applying a slab selection gradient to a subject by a gradient output module; transmitting a radiofrequency (RF) pulse to the subject by a RF excitation module, and exciting a slab of the subject to produce a plurality of magnetic resonance signals with a continuous frequency bandwidth; performing a spatial encoding gradient across three dimensions by the gradient output module to encode the magnetic resonance signals, wherein an equivalent encoded field of view along a selected acceleration direction is controlled by the spatial encoding gradient, and is made shorter than an excited slab size and the equivalent encoded field of view along an image separation direction expands; applying a separation gradient (G sep ) along with the spatial encoding gradient (G spen ) by the gradient output module to produce a plurality of encoded resonance signals; and receiving the encoded magnetic resonance signals by an RF receiving module, and reconstructing the encoded magnetic resonance signals into a 3D image space by an imaging processing module.