The invention provides a manufacturing method of a thermoplastic resin composition containing cellulose fiber that can obtain the cellulose fiber containing defibrinated fiber. More particularly, the invention provides the manufacturing method of the thermoplastic resin composition containing the cellulose fiber, and the method comprises the following processes: the process that the cellulose fiber aggregations are put into a mixer with rotation blades that are taken as stirring devices, and the cellulose fiber aggregations are defibrinated by high-speed stirring; the process that the thermoplastic resin is stirred after being put into the mixer, therefore, the thermoplastic resin is melted by the generated friction heat, and the mixture that the thermoplastic resin is attached on the defibrinated cellulose fiber is obtained; and the process that the mixture is cooled while the low speed stirring is operated.