To study the distribution characteristics of explosion overpressure field for non-circular cross-section cloud, the numerical simulation of overpressure process of cloud explosion was performed by LS-DYNA program. Comparison between the simulated overpressure values with experimental was carried out. The changing rule of overpressure with distance, as well as of different ignition height on overpressure field distribution was studied at four directions, including 0°, 90°, 135° and 180°. Results show that: ignited cloud shows up as an ellipsoidal detonation fireball in experiment. The peak overpressure value measured at the position of 5 m from explosion center at four directions is from 2.9 MPa to 5.2 MPa. In the range of 5 m to 50 m from explosion center, a shock wave oval trajectory on ground was revealed. Shock wave propagated at 90° direction has lower velocity than others. In the range of 5 m to 15 m, the ground peak overpressure enhances by 8% averagely when ignited height increases from 0.5 m to 2.5 m.