The multi-alkali photocathode （Rb

Cs） Na2KSb films are studied. The photo-cathode manufactured by means of a new technology has many advantages over the trialkali photocathode

such as higher photosensitivity

better reproducibility

less thermal emission and

particularly

much improved response to light in the green-red-infrared portion of the spectrum

photoelectron-emissive mechanism of the photocathode films are discussed and a new strcture model of energy bands at surface of the of the （Rb

Cs） Na2KSb is proposed. The use of the model to explain the result of the experiment is satisfactory.