Current differential protection (CDP) is introduced into active distribution networks (ADNs) to improve the protection reliability. However, the complex fault characteristics of ADNs lead to degradation of the CDP performance. In addition, it is difficult for CDP to satisfy the requirements of various scenarios for protection. Under this context, this study proposes a pilot protection method based on the phase-space trajectory of quasi-power (PSTQP). First, the feasibility of the quasi-power theorem to be used in ADNs is analyzed. Second, the quasi-power is selected as the one-dimensional time series for phase-space reconstruction, and the characteristics of the PSTQP under internal and external faults are analyzed. Finally, two protection criteria are designed according to the requirements of different protection scenarios. The PSCAD/EMTDC-based simulation results verify that the designed protection criteria are effective for various fault conditions. Furthermore, the high-speed protection scheme can shorten the fault duration, and the protection scheme for immune to synchronization errors can reduce dependence on data synchronization and eliminate the requirement for additional synchronization devices.