The invention relates to a flexible grid connection method and a flexible grid connection device for a rectification-side current transformer. The method comprises the steps of acquiring a three-phase voltage signal input by a power grid in real time; determining a phase angle of the three-phase voltage signal by coordinate transformation; and when a deviation between the phase angle of the three-phase voltage signal and the best switch angle is within a set range, driving the rectification-side current transformer to be connected into the power grid. According to the method and the device provided by the invention, the phase angle of grid connection is controlled according to a predetermined strategy based on the phase angle of the three-phase voltage signal input by the power grid in real time, namely when the deviation between the phase angle of the three-phase voltage signal input by the power grid in real time and the best switch angle is within the set range, the rectification-side current transformer is driven to be connected into the power grid, at the moment, a minimal difference is achieved between amplitudes of a three-phase output voltage of the rectification-side current transformer and a three-phase voltage of the power grid, and a grid connection surge current is also small. Therefore, according to the method and the device provided by the invention, the surge current during a grid connection process of the rectification-side current transformer can be effectively reduced, and the purpose of flexible grid connection is achieved.