Accelerator beam emittance is an important parameter of beam quality, and it describes the beam’s radial performance. The paper describes the doubleslit scan measurement principle and method of the accelerator beam emittance, and designs a control and measurement method of doubleslit scan based on PXI system and LabVIEW software for achieving realtime measurement of emittance. Combined with the research need of China Spallation Neutron Source project beam halo, using stepper motor control doubleslit scan: with every movement completion by one step of position slit, the angle slit exercises a radial distance; with moving one step of the angle slit, the DAQ work one time for beam signal and the two slits’ position information, and the resulting data is processed finally. The method meets to project’ needs, and is verified in Median Energy Beam Transform and Low Energy Beam Transform of China Spallation Neutron Source project.