The present invention provides a thermoplastic resin film which has uniform optical properties and can be used for a high quality functional film and a method for producing the same to suppress uneven thickness in the machine direction of a film and streaks in the film. The method for producing a cellulose acylate film (12), includes the steps of melting a thermoplastic resin in a single screw extruder (22), discharging and feeding the molten resin to a die (24) through the extruder (22), extruding the molten resin from the die (24) in the form of a sheet, and solidifying the molten resin by cooling, wherein the extruder has a feed section (A), a compression section (B) and a metering section (C) and transport efficiency .eta.F of the thermoplastic resin in the feed section (A) is 0.2 to 0.7.