1. An optical imaging method using a single-pixel detector, an image of a target object is expressed by using a matrix of M×N pixels; the actual size of the scene constituting the target object is in the shape of a rectangle having a size of Mδ x ×Nδ y , where M and N are positive integers, and δ x ×δ y is a geometrical dimension of one pixel in x and y direction, characterized in that the method comprising: generating a sequence of light fields having different spatial frequency and initial phase by a structured light field generator; wherein the intensity of the light fields is distributed according to a cosine function; the light intensity distribution of a light field in the target object plane is P(x, y; f x , f y )=a+b·cos(2πf x x+2πf x x+2πf y y+φ), wherein a is a mean intensity of the light field; b is a contrast; a and b are positive numbers; x and y are pixel coordinates in the target object plane, x is an integer between 0˜M−1, y is an integer between 0˜N−1; f x and f y are respectively frequencies in x and y direction, f x and f y are normalized to be α M and β N ; where α is an integer between 0˜M−1, and β is an integer between 0˜N−1; φ is an initial phase; each spatial frequency pair (f x , f y ) corresponds to at least three different initial phase φ values; illuminating light fields onto the target object sequentially; wherein the intensity of the light fields is distributed according to a cosine function with different frequency and different initial phase; receiving light signals sequentially from the target object by an single-pixel detector and then collecting and recording response values of the single-pixel detector; obtaining the Fourier spectrum D fp (f x , f y ) of the image of the target object according to the response values; and applying a two-dimensional discrete inverse Fourier transform is to spectrum D fp (f x , f y ) to reconstruct the image of the target object I(x, y).