The condition of smooth temporal and spatial change of ionosphere should be demanded in all the methods to estimate the GPS Differential Code Bias (DCB) from GPS observation. Nevertheless, because the ionosphere usually exhibits variation to different degrees, this condition is just an approximation. Therefore, it can be indicated that the stability of GPS DCB estimated from GPS observation is affected by the ionospheric status. With SCORE DCB estimation method and GPS data obtained at BJFS (middle latitude) and XIAM (low latitude) stations in 2001 and 2009, the satellites DCBs are estimated respectively. Especially, the influence of ionospheric diurnal variation on the DCB stability is verified. It is found that the condition of the ionospheric diurnal variation affects the stability of satellites DCBs estimated from GPS observations, and the satellite DCBs estimated from nighttime GPS data are more stable than that from daytime data. The stabilities of estimated DCBs from BJFS data in 2001 and 2009, and those from XIAM data in 2009 exhibit heavy dependence on local time, but the difference is not obvious for the DCBs estimated from XIAM data in 2001. XIAM station is located near the equatorial ionospheric anomaly, and the ionosphere of this region exhibits notable variations even in the nighttime in solar maximum phase. This may be the reason for the weak dependence of estimated DCBs on local time.