Experiments were performed to investigate the detonation behaviors of stoichiometric hydrogen-oxygen mixtures (at sub-atmospherical pressures) in annular tubes with circular obstacles. The annular tube was 1000 mm long and 48 mm in diameter (D). The circular obstacles were with the diameters of 37.20 mm and 30.36 mm, corresponding to the BR = 0.57, 0.36 (BR: blockage ratio), respectively. Two types of obstacle spacing S was set in the test, which are S = D and S = 2D. The detonation velocities were obtained based on the time of arrival of the wave front monitored by pressure transducers. Smoked foils were used to register the detonation cellular evolution though the test section. The results showed that the propagation limit in this test was 2ω/λ≈1(ω indicates the channel width, λ represents the cell width), which was consistent with the previous results in round tubes with orifice plates. The obstacle spacing presented no noticeable effect on detonation propagation limit. However, it played a significant role on detonation velocity. What is more, larger flow blockage for BR = 0.57 caused the more violent velocity fluctuation and higher propagation limit than in smaller blocking ratio. The process of diffraction-retonation for interaction between wave front and obstacle was analyzed in detail. In further, special vertical bands with periodic variation characteristic were observed between two adjacent obstacles. The vertical bands were spaced as same as the obstacle spacing and attached very fine cells which were caused by the head-on collision of the detonation wave propagating in the compressed region with high temperature and pressure.