In high band rate optical communication systems such as 40 Gbps system,dispersion fluctuation caused by factors such as temperature change and power variation is beyond the dispersion tolerance.To compensate for these dispersion fluctuations,tunable dispersion compensators (TDCs) are needed.Various types of tunable dispersion compensators have been demonstrated in this paper，such as CFBG,VIPA,G-T interferometer,AWG and PLC.The operating principle and characteristics of these techniques are analyzed,and the developing trend of TDCs are also discussed briefly.