Abstract: In order to design a photonic crystal waveguide which can propagate slow light with wide band and low dispersion, on the basis of photonic crystal structure of triangular lattice dielectric cylinder, the periodic arrangement was carried out using circular scatterers and elliptic scatterers. Plane wave expansion method was used to simulate the designed coupled cavity waveguide. The results show that the maximum group velocity of guided mode decreases from 0.035c to 0.01c by changing long axis R_a of oval scatterers in defect line. The group velocity can be further decreased when short axis R_b in defect line is changed. Further study shows that by changing area ratio of two scatterers of the first row around the microcavity, the maximum group velocity is reduced to 0.0065c, and low dispersion slow light with wavelength range of 3.25nm was gotten. When the designed coupled cavity was used in optical buffer, cache time of 76.82ps and the maximum ache capacity of 15.56bit can be achieved. The research has reference value in the design and application of novel devices based on photonic crystal waveguides.