Abstract: A high-current ion beam emittance measurement unit (EMU) is introduced in the paper. The measurement principle of slit-wire method is discussed. The system construction and design key-points of the EMU are discussed, too. The measurement results of emittance of ECR proton source at China Institute of Atomic Energy using the EMU were given. For high-current ion beam, short slits have to be used to sample part of beam so that effective cooling could be performed, which would introduce some systematic errors and its correction could be estimated by simulation.