Abstract: A compact ECR source with a unique magnetic field configuration is described. The resonance magnetic field is generated by electromagnetic coil and iron circuit. With the adjustable magnetic field, the ion source can operates in optimal condition. A 35 mA hydrogen beam has been extracted from a 4 mm aperture of the source with about 550 W microwave power. The proton ratio of the beam is over 90 %. Other ion species (7 mA O +, 8 mA N +, 12 mA Ar +) are also extracted from this source.