The characteristics of slow light in the 2D triangular rods photonic crystal line defected waveguide have been investigated with plane wave expansion (PWE) method. It is found that the filling factor of the photonic crystal and the radius of defect rods decide the propagating characteristic of the guided mode in the photonic crystal band gap. The group velocity of the guided mode decreases rapidly as increasing the filling factor. The effect of radius of the defect rods on the group velocity is stronger than the former. The waveguide structure with group velocity smaller than 0.01c is demonstrated through detuning the filling factor and defect rods size. Group velocity dispersion (GVD) of the slow light is analyzed, and it is found that the magnitude of GVD value in the area of ultra slow light is about 105～106 and propagation with high efficiency can be guaranteed.