As a piece of power flow control equipment, the symmetrical dual core phase shifting transformer (PST) can realize the control of transmission power of a transmission line. However, after the PST is connected to the line, the line impedance distribution, voltage and current signals will be changed. This may lead to misoperation or refusal of distance protection. In order to eliminate the influence of PST access on conventional distance protection, given the phase-shifting characteristics of a PST on fault components of each sequence networks, the equivalent impedance of PST sequence networks and the algorithm of grounding and phase-to-phase measurement impedance are used. It is deduced that the PST installation position, PST phase-shifting angle and fault position will affect distance protection. Based on the influence mechanism of distance protection by PST access, an adaptive distance protection based on phase angle compensation and phasor measurement units (PMUs) is proposed. This uses symmetrical component inverse transformation and synchronous phasor measurement technology. The PST model is built using Matlab/Simulink, and the correctness of the derivation of the influence mechanism of PST access on distance protection and the effectiveness of the proposed adaptive distance protection improvement measures are verified by simulation. This provides theoretical support for the in-depth research and engineering application of a PST in the future. This work is supported by the National Natural Science Foundation of China (No. 51567005).