Radio over fiber (RoF) system is a research hotspot of optical communication in recent years. Suppressing the three order intermodulation and improving spurious-free dynamic range are (SFDR) important optimization objectives in RoF system. In order to improve the dynamic range of RoF system, a new scheme which is based on a fiber Bragg grating notch filter and a tunable delay line (TDL) to realize the three order intermodulation suppression is proposed. After theory analysis to this scheme, an experiment is made to verify it. The experimental results show that it can effectively suppress the three order intermodulation and improve the system's dynamic range by 10.5 dB. In addition, this scheme has the advantages of simple structure and low cost.