Abstract: The CYCIAE-230 cyclotron is a proton beam accelerator that is dedicated to proton therapy. In order to meet the requirement of the cavity Dee voltage stability, RF frequency stability and acceleration voltage amplitude balance of the accelerator RF system, a set of low level RF (LLRF) system including the digital-analogue type amplitude loop, the digital tuned loop and the digital voltage balance loop was developed. The LLRF system communicates with the host computer through the serial port to realize the local debugging, and the communication between the LLRF system and the PLC network is realized by using the Profibus-DP communication protocol. The low power desktop experiment and the joint debugging were completed on an experimental cavity with a reduced scale oxygen-free copper. The validity of the voltage balance algorithm was validated, and a key start of the LLRF system was realized without human intervention. The LLRF system satisfies the demand of high frequency system.