1. A Gaussian beam migration imaging method, comprising:representing, by a computing device based on execution of instructions stored in a computer readable medium, a seismic wave field of an earth surface in a form of superposition of Gaussian beams with a preset curvature parameter in time-space domain, wherein the representation of the seismic wave field of the earth surface comprises a waveform function and a time-space domain Gaussian beam based function;

setting, by the computing device based on execution of the instructions stored in the computer readable medium, a width of a Gaussian beam based function of the seismic wave field of the earth surface as a preset width, and setting a spacing between centers of adjacent Gaussian beams of the seismic wave field of the earth surface as a preset spacing, so as to obtain a set seismic wave field of the earth surface;

establishing, by the computing device based on execution of the instructions stored in the computer readable medium and according to the set seismic wave field of the earth surface, a decomposition model for the seismic wave field of the earth surface; and

applying, by the computing device based on execution of the instructions stored in the computer readable medium and based on seismic data and a medium velocity model, an optimization solution algorithm to the decomposition model for the seismic wave field of the earth surface, so as to obtain a plurality of waveform functions corresponding to the seismic data; and

propagating, by the computing device based on execution of the instructions stored in the computer readable medium and based on the medium velocity model, Gaussian beams corresponding to the plurality of waveform functions, and performing migration imaging to obtain migration imaging results,

wherein the step of representing a seismic wave field of an earth surface in a form of superposition of Gaussian beams with a preset curvature parameter in time-space domain comprises:

obtaining, according to a two-dimensional seismic acoustic wave equation, an approximate solution of the two-dimensional seismic acoustic wave equation under an assumed high-frequency condition, the obtained approximate solution representing a Gaussian beam with a curvature parameter;

setting the curvature parameter of the Gaussian beam with a curvature parameter of an earth surface as a preset curvature parameter, and superposing, by using spectrum functions with the preset curvature parameter as superposition factors, a plurality of Gaussian beams with the preset curvature parameter of the earth surface with the plurality of Gaussian beams having different parameters, so as to obtain a frequency domain seismic wave field of the earth surface represented in a form of superposition of the Gaussian beams with the preset curvature parameter;

transforming the Gaussian beams of the frequency domain seismic wave field of the earth surface into time domain Gaussian beam based functions, and transforming the spectrum functions of the frequency domain seismic wave field of the earth surface into waveform functions, so as to obtain a time domain seismic wave field of the earth surface; and transforming the time domain Gaussian beam based functions of the time domain seismic wave field of the earth surface into time-space domain Gaussian beam based functions, so as to obtain the seismic wave field of the earth surface represented in a form of superposition of Gaussian beams with the preset curvature parameter in time-space domain.