This paper describes the design of an apparatus for measureing electron momentum distributions and Fermi surfaces in solids. This apparatus can also be used in positronium chemistry and other positron studies. The vertical long-slit geometry was adopted. The central distance between the specimen and the slit was 3 meters. A typical geometric angular resolution of the system is 0.33Mrad. The positron source was

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Na with an activity of 30 mCi. Annihilation photons with an energy of 511keV were detected by the NaI (Tl) scintillation detectors of 300mm long. The conventional fast-slow coincidence was employed for the nuclear measurement system. Experimentally

the operation can be performed by a simple automatic way.