In electric vehicle (EV) charging stations equipped with shunt active power filters (APFs), the operation of the shunt APF may amplify (harmonic amplification) the charging current harmonics at the point of power collection. This paper focuses on an EV charging station with three-phase uncontrolled rectification chargers that produces the most serious harmonic pollution. By analyzing the coupling relationship between harmonic current and voltage of EV charging stations, as well as by defining the total harmonic current amplification factor, this paper proposes an analytical method to quantify the amplification degree of charging current at the point of power collection. On this basis, the variation trends show how the amplification factor changes with key parameters, such as quantity of chargers, compensation rate, and compensation phase difference of APFs are discussed. The results are beneficial to gaining further understanding on capacity correction and control design of APFs in an EV charging station.