The value of voltage in dc link of parallel-type active power filters（PAPFs） is directly influencing the performance of compensation. An extensive analysis of compensation characteristics in PAPF is carried out. First， respectively in the single-phase system and the three-phase system for load current of a thyristor rectifier with resistive and inductive load， the theoretic minimum of voltage in dc link for harmonic full compensation is obtained through equivalent circuits analysis. Then， when voltage in dc link is smaller than the theoretic minimum and under sinusoidal pulse width modulation control strategy， the quantitative relationship between the total harmonic distortion（THD） of current after compensation and voltage in dc link is also elaborated by using the simulation curves. With these curves， the selection of voltage rated value in dc link for PAPF is quite straight forward. The simulation and experimental results verify the correction of selected voltage in dc link.