A system and a method for CIGS thin film pretreatment are provided by the invention. The system includes a RF power supply, an inductance coil, a process chamber, adaptation modules, a cathode plate and a quartz cover. The inductance coil is circumferentially disposed on a top of the process chamber. The cathode plate is disposed at a bottom of the process chamber. A substrate is disposed between the inductance coil and the cathode plate. The RF power supply includes a first power supply and a second power supply, wherein the first power supply powers the inductance coil via the adaptation module, and the second power supply powers the cathode plate via the adaptation module. Rays formed by the inductance coil enter the process chamber through the quartz cover under an action of the RF voltage, so that a process gas in the process chamber forms plasma. The plasma moves towards the cathode plate and bombards an uneven region of a CIGS thin film on the substrate under the action of the voltage, so as to flatten the CIGS thin film.