In the passive ＲFID (radio frequency identification) system，the backscatter powers of tags is affected by the path loss and causes the capture effect. The capture effect will make some tags be hidden and reduce the efficiency of identification. In this paper，we propose an improved anti-collision algorithm capture effect tags optimization grouping(CEOG). We research the captures effect of system，use Chebyshev to estimate the number of tags and the probability of capture，and the tags are grouped by the capture effect optimization grouping. By the theory analysis and simulations，the CEOG can make the system throughput exceed 60%.