The Korean 4th Generation Storage Ring (4GSR) project is being developed with the goal of commissioning at the end of 2027. The facility aims to generate the ultra-low emittance beam with the beam current of 400 mA and the beam energy of 4 GeV. To accelerate and store the beam to desired parameter, 500 MHz normal cavity, high power RF amplifer and digital Low Level RF (LLRF) system will be installed in the main ring. This paper describes the design study about the LLRF prototype system for digital feedback control and overview of the RF signal processing schemes. In addition, the performance test result about traditional feld control algorithms associated to the LLRF system will be presented.