The invention belongs to the technical field of digital signal processing, and relates to a high-accuracy instantaneous phase estimation method based on the full-phase FFT. The steps of the estimation method comprise directly sampling an input signal x(t) to obtain a discrete data sequence (x(n-N+1)..., x(n), ..., x(n+N-1)), storing 2N-1 data obtained by sampling in the RAM of a DSP, utilizing a convolution window of which the length is 2N-1 in number to perform windowing for the sequence, superimposing the data of which the distance is N sampling intervals, fast performing Fourier transformation to the N data, outputting N plurals which namely correspond as N spectral values Y(k), performing spectral peak searching, finding a spectral Y(k*) with the highest amplitude in the N spectral values Y(k), and performing rating to the imaginary part and the real part of the spectral Y(k*), thereby an instantaneous phase estimation result of a time n can be obtained by performing arctangent calculation to the ratio.