Disclosed is a transformer inrush current identification method based on phase space reconstruction of a differential current polar coordinate system. The method includes the following steps: among Npoints every cycle, collecting secondary currents of current transformers on both sides of transformer differential protection and forming a differential current signal sequence I; judging whether a value of the differential current signal sequence I exceeds a setting value of a differential protection start-up element, and adopting criteria provided by the invention to judge false differential currents and inrush currents if the value of the differential current signal sequence I exceeds the setting value; reconstructing the differential current signal sequence into a two-dimensional phase space with a delay time of 1/4 period, converting the sequence into a polar coordinate form, taking the number n of points of polar angles within a specified range in a one-cycle wave phase space trajectory as a criterion of protection motion, comparing n with a set threshold value nset, performing protection motion if n>nset, otherwise, performing protection blocking. The method can accurately judge CT saturation of faults in a region, inrush currents and faults outside the region, thus ensuring the reliability of differential protection.