The significant effect factor of slow light transmission in photonic crystal coupled resonator optical waveguide is investigated.The change tendency of guided mode band,group velocity and group delay with the tuning of distance between neighboring cavities are discussed.The guided mode is flattened clearly and the group velocity decreases sharply with the increasing of cavities distance.When the interval between contiguous cavities is 7 lattice constants of photonic crystal,the ultra small group velocity below 2×10-4c is obtained.This is roughly two orders of magnitude smaller than that in line defect PC waveguide.The maximal group delay through CROW of 13.23 μm with supercell 7×7 exceeds 400 ps,which are four orders of magnitude larger than that in traditional waveguide with the same length.