Based on slow light theory and nonlinear coupled-mode equations of fiber Bragg grating, the characteristics of the velocity when Bragg grating (BG) solitons transmitting through fiber Bragg grating (FBG) are simulated. The time delay of the BG solitons is measured by an experimental system, which based on the high-speed oscilloscope. The time delay of the high-intensity narrow pulses propagating in the BG is acquired. The results show that, with BG on ordinary signal-mode fiber of 5 cm long, the time-delay is 426 ps and its speed is 1.17×108 m/s, and that in other case, when the fiber has high nonlinearity, the time delay is 1.639 ns, and the speed of the BG soliton is 0.31×108 m/s. Thus, the deceleration of the BG soliton is possible, and the velocity with that the soliton tansmitts through the high nonlinear FBG is lower than that through the ordinary signal-mode FBG.