A method based on finite difference time domain (FDTD) is applied to calculate the photonic crystal fiber (PCF). Some problems by using FDTD have been pointed out, especially the distribution of mesh and set to the properties of PML. A dual-concentric-core photonic crystal fiber based on pure silica has been analyzed by the proposed method. The transmission characteristic of such PCF has been deeply numerically simulated. By adjusting the structural parameters, we designed broadband dispersion compensating PCFs (DCPCFs) with large negative dispersion values. Simulation results show that the dispersion values vary between -400 and -600 ps/(nm·km) over the C band (from 1530 to 1565 nm), which is 5 times larger than the conventional dispersion compensating fibers (DCF) with nearly equal effective mode area. It can effectively compensate for the dispersion of 25 times of its length of standard single-mode fiber (SMF) with residual dispersion below ±1.0 ps/(nm·km) over the entire C band. It is very useful of such PCFs to be applied in leap optical amplifiers with high gain and dispersion compensation functionalities in a single component.