Variable dc-link voltage control methods can effectively improve the operation efficiency of the permanent magnet synchronous motor (PMSM) drive system. At present, the reported variable dc-link voltage control methods applied in the PMSM driven by quasi-Z-source inverter (qZSI) are limited to analytical calculation methods (ACMs) based on system model. The ACMs demand measurement of qZSI’s input voltage and usually need a larger margin index due to the inaccurate model to calculate the reference dc-link voltage. To overcome the restriction, this project proposes a novel variable dc-link voltage control method which can indirectly adjust dc-link voltage with an extra PI-regulator. Basic principle of the method is introduced and two design rules of the PI-regulator are illustrated. Besides, necessary conditions which need to be met when obtaining the feedback signal of the PI-regulator are analyzed. Finally, experiments are performed to validate the feasibility and effectiveness of the proposed method. In comparison with the ACMs, the proposed method gets rid of the dependence on an extra voltage sensor to measure the input voltage and can reserve fewer margins for the dc-link voltage, which contributes to less cost and higher efficiency of the drive system. Besides, the proposed method is easy and convenient to apply.