A device for treating high density organic waste water by a multiphase photocatalysis combined film bioreactor, comprises a filter, a primary photocatalyst reactor, a secondary photocatalyst reactor, an acidifying hydrolysis pool, and a film bioreactor; wherein a pipeline is communicated among the filter, the primary photocatalyst reactor, the secondary photocatalyst reactor, the acidifying hydrolysis pool, and the film bioreactor. High density organic matters, under action of ultraviolet light and a catalyst, can be rapidly degraded to be innocuous and unpoisonous small molecules such as CO2, H2O, etc. The device and the method have advantages of: (1) fast catalytic reaction speed, stay time of organic sewage in a photocatalytic reactor can be controlled in 4h; (2) non-selectivity degradation: comprising difficultly-degraded organic matters like chlorinated organic compounds and polycyclic aromatic hydrocarbons; (3) no secondary pollution: the organic matters are thoroughly differentiated and degraded to be harmless substances such as CO2, H2O, etc.; (4) wide application range: the device and the method can almost be applied on all organic sewage, such as papermaking waste water, printing waste water, pesticide waste water, etc., and (5) combination with an MBR film bioreactor technology, small system equipment investment and low operation cost.