The invention discloses a single-period double-correction power-frequency software phase-locked loop method. The single-period double-correction power-frequency software phase-locked loop method comprises an analogue-to-digital conversion step which comprises that an analogue-digital converter collects three-phase voltage signals or three-phase current signals, namely input signals f (t), of a three-line power line and generates into digital signals which are output to a frequency corrector after analogue-to-digital conversion; a frequency correction step which comprises that the frequency corrector corrects frequency according to the input digital signals and a fundamental component omega0t of the input signals f (t), obtains phase-locked signals with the same frequency-locking signals as the fundamental component omega0t of the input signals f (t) and outputs to an initial phase corrector; an initial phase correction step which comprises that the initial phase corrector corrects the initial phase according to the input frequency locking signals and the fundamental component omega0t of the input signal f (t), obtains phase signals omegat+theta with the same frequency and the initial phase as the fundamental component of the input signals f (t) and accordingly achieves track of the fundamental component omega0t of the input signals.