The present invention discloses a harmonic current estimation method based on an improved FastICA algorithm. The harmonic current estimation method is characterized in that a quasi-Newton method is adopted to replace a Newton method as an optimization method of FastICA. The present invention has the beneficial effects that (1) harmonic currents in a power grid can be accurately estimated in the condition of unknown harmonic impedance; (2) the problems that a harmonic measuring device is difficultly obtained by the actual harmonic impedance of a system, and the cost is great are overcome; and (3) compared to the original method, the harmonic current estimation method is capable of improving the accuracy of the algorithm and better solving the problem that the harmonic impedance is difficult to determine.