Data center power systems tend to have more severe harmonic distortions when boost power factor correction (PFC) converters operate with light loads. The conventional harmonic damping method that increases the input conductance of PFC converter becomes less effective, due to the reverse blocking of the front-end diode rectifier in the PFC converter. To tackle this challenge, this article proposes an adaptive harmonic conductance control (AHCC) that can automatically achieve maximum harmonic mitigation for PFC converters at light loads, and no extra sensor is needed. In this approach, the critical value of harmonic conductance, beyond which the harmonic distortion is inversely amplified by the reverse blocking of diode rectifier, is identified first. Then, a method for online detection of the critical harmonic conductance is developed, which ensures the minimum harmonic distortion of PFC converters at light loads. Finally, the effectiveness of the AHCC approach is validated by experimental tests of 0.9 kW boost PFC converter modules under varying loads, distorted grid voltages, and paralleled operations.