The invention provides a power flow division type acceleration gearbox capable of being used for a 6-8MW semi-direct driving wind generation set. The power flow division type acceleration gearbox is formed by connecting a composite planet wheel differential wheel system and an NGW wheel system fixed with a planet wheel shaft in parallel, wherein a gear ring in the differential wheel system is connected with a center outer gear of the NGW through a spline, and the input power is divided at the inner gear ring part of the NGW and a planet frame of the differential wheel system, and is transmitted to an output shaft after being gathered at a sun wheel part of the differential wheel system. The power flow division type acceleration gearbox has the advantages that the input power flow division and flow merging can be realized, so that the load borne by each gear can be reduced; a low-speed-stage fixed shaft wheel system is arranged behind a high-speed-stage different wheel system, so that the integral structure of the gearbox is more compact; through the planet gear duplex gear design of the composite planet wheel differential wheel system, and the medium-speed power generator input rotating speed requirements can be met. The power flow division type acceleration gearbox disclosed by the invention is applied to the 6-8MW semi-direct driving wind generation set, and has the characteristics of high bearing capability, compact structure, small size, small weight and the like.