Shanghai soft X-ray free electron laser facility (SXFEL) is the first fourth generation light source in China, and its shortest wavelength can reach 2 nm. The facility consists of an injector including an S-band photocathode Radio Frequency (RF) gun, two S-band accelerating sections and one main accelerating section including six C-band accelerating sections. In the low level radio frequency (LLRF) system, C-band microwave system operates at 5712 MHz. C-band microwave signals are mixed with the 5686.556 MHZ local oscillator (LO) signal on the RF front-end board and down converted to 26.444 MHz intermediate frequency (IF) signal, and then sampled by 105.778 MHz clock signal. According to the physical design requirements of SXFEL, DWC8VM1 board based on MTCA platform is selected as the RF front-end board of LLRF system. In this paper, the parameters of the RF front-end such as isolation between RF input ports, input and output linearity, amplitude and phase stability and Additional phase noise of up conversion channel were experimentally tested. The experimental results show that input return loss is more than 8.63 dB, channel-to-channel crosstalk is more 63 dB and the additional phase jitter integral of up conversion channel is 2 fs. The performance of this RF front-end (DWC8VM1) can meet the theoretical requirement of the SXFEL.