Abstract: The SHINE based on the superconducting linear accelerator is the first quasi-continuous wave hard X-ray free electron laser user facility under construction in China. It has the characteristics of high repetition rate of 1 MHz max, low bunch charge about 100 pC and large scale about 3.1 km. In order to reduce the decay of the output power of FEL radiation, it requires a beam position monitor (BPM) system with resolution of two hundred nanometers to realize the close interaction and energy exchange between the electron beam and the photon beam in the undulator. The BPM system that has been developed for SXFEL cannot fully meet the requirements. Therefore, based on the quantitative relationship between the relative amplitude extraction uncertainty of the cavity BPM signal and the main parameters of each subsystem, as well as the reasonable allocation of key technical indicators, a prototype of cavity BPM system was designed and developed, which consists of a Cband cavity BPM pickup, a radio frequency (RF) front-end with the character of signal-channel down converted RF signal to low intermediate frequency (IF) signal and low noise figure, and a dedicated digital BPM signal processor. As a bridge between the cavity pickup and the digital BPM signal processor, the structure and performance of the RF frontend also determine the performance of the CBPM system directly. In this paper, based on the SHINE’s demand for cavity BPM system, the key technical indicators of the RF frontend were analyzed, the scheme of amplifier switching type RF frontend was proposed, and the advantages of the RF frontend schemes with amplifier switching type and the adjustable attenuation type were compared and analyzed by the method of parametric simulation. And an offline full phaselocked sampling test bench which can simulate beam conditions is also successfully built for the first time. In addition, the beam test bench was built in SXFEL facility and the performance evaluation of the RF frontend was completed. Based on the evaluation method of power divided, the experiment results show that the position resolution can reach 71 nm under the condition of bunch charge of 100 pC and the system dynamic range of ±100 μm, which is consistent with the theoretical value and better than the design requirement of the SHINE.