Effect of heavy ion irradiation was investigated for DyBCO coated conductor fabricated by ISD (inclined substrate deposition) process to study the flux pinning property by columnar defects. It was found that the critical current density in the specimen with large columnar defects increased sufficiently at high magnetic fields. On the other hand, the enhancement of the critical current density was not sufficient for the case of small columnar defects. The obtained results were analyzed using the flux creep-flow model and the most probable value of the virtual critical current density in the ideal creep free case was estimated for columnar defects. These results were compared with the value expected by the statistical summation theory and agreement was obtained. This theoretical result predicts that introduction of columnar defects with larger radius of higher density is effective for improvement of the critical current density.