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A 325-MHz continuous-wave (CW) four-vane radiofrequency quadrupole (RFQ) is employed in Injector-I of the China Accelerator-Driven Subcritical System. The radiofrequency tuning and beam commissioning were performed from January 2014 to January 2017. In a cold test, a stability study showed that the design of the seg-mented resonantly coupling and dipole stabilizer rods can shift the harmful quadrupole and dipole mode from the fundamental mode to above 2.6 MHz. We also found a simplified tuning method for the field unflatness, involving changing the inserted length of a few plug tuners. For achieving CW-beam commissioning, two full-size RFQs were constructed successively. The commissioning results indicate that the beam transmission rate decreased by approximately 3％ as the normalized field unflatness decreased by 1％. A 10-MeV CW proton beam with an average beam current of 2.1 mA was achieved at the target of Injector-I, and the output beam energy of the RFQ was 3.18 MeV.