We report the design and analysis of a rod-type photonic crystal fiber with Er-Yb co-doped for the high power 1.5-μm band amplifier. The fiber structure is designed to be the 120-μm extreme large core diameter, 300-μm inner cladding diameter, and 1.5-mm outer cladding diameter that ensure the single mode output during high power amplification. Both the continuous wave (CW) and pulsed amplification characteristics are analyzed based on the exact modeling and simulation under the designed geometry. The 4-mJ pulse energy and 400-kW peak power are obtained in theory, so the 1.5-μm band amplifier that achieves milojoule level pulse energy meanwhile keeping single mode is firstly designed.