Abstract: Compared with traditional radar or communication devices, the integrated radar and communication system is easy to be integrated and smaller with higher spectrum efficiency, in which the linear frequency modulation (LFM) based integrated system is widely used. In term of realizing the communication function, the traditional synchronization scheme will reduce the data rate. Thus, an integrated signal consisting of two LFM carriers is designed. Then, a Costas loop-based joint time and carrier frequency synchronization is proposed by using the good autocorrelation of LFM. The proposed synchronization method contains two steps. First, a LFM based Costas loop is designed to track two LFM carriers. Second, the delay and carrier frequency offset are retrieved from the frequency of these two carriers. Simulation results show that the proposed technique can realize the joint time-frequency synchronization without affecting the communication efficiency and radar performance, and the bit error rate is comparable to that of traditional synchronization technique.