We report a large mode area photonic crystal fiber with a top-hat mode field. The optical fiber has a multi-layer square structure with air holes and doped layer. A flat and top-hat-like mode intensity profile is provided through the reasonable design of the doped layer. The modal characteristics including effective mode area, dispersion and confinement loss are investigated. The proposed fiber with a top-hat mode generation may have potential applications in laser drilling, laser cleaning, imaging, spectroscopy, and so on.