In order to eliminate the effects of ionospheric delay, navigation satellites usually launch multiple frequency navigation signals, such as BeiDou satellite navigation system which launches three frequency point signals of B1, B2 and B3. Because of the differences of each frequency channel of satellite which transmit navigation signals, the hardware delay of each frequency channel is not the same as the other, which called TGD (Total Group Delay). Similarly, there are differences between the delays of different frequency channel of the receiver, which called IFB (Inter Frequency Bias). The combination delay bias containing TGD and IFB that called DCB (Differential Code Bias) as a crucial parameter in GNSS has an important effect on the precision of navigation positioning, orbiting and timing. Moreover, it is a primary error of ionospheric delay modeling. Along with the development of high-precision technique of navigation positioning and timing, the research on Differential Code Bias of GNSS is more and more important. At first, the definition of DCB of BeiDou satellite navigation system is briefly described, then the test method of DCB is put forward. And then, the short-term and medium-and-long-term variation characteristic of DCB of GEO satellite is analyzed using the observation data of BeiDou receiver of three months. At the same time, in order to eliminate the impact of receiver hardware delay, a difference operation has been done between satellites' DCB, the indirect analysis result of variation characteristics of the hardware delay of GEO satellite is obtained. The results show that the combination hardware delay bias of GEO satellite in BeiDou system is stable during the medium and long term, the variation range after smoothing process is smaller than 2 ns. It also indirectly shows that GEO satellite hardware delay of BeiDou system has a good medium-and-long-term stability.