The utility model provides an eight fast double clutch speed change gear belongs to derailleur technical field. This speed change gear includes primary input axle, an input device, the 2nd input device, double clutch, an output device, the 2nd output device, the 3rd output device and a plurality of synchronous ware. An input device includes first input shaft and three odd number shelves driving gear, and the 2nd input device includes second input shaft and two even number shelves driving gears, and an output device includes first output shaft and sets up four driven gear in first output shaft department. In the three odd number shelves driving gear one be with the sharing driving gear of two driven gear meshings, each of two even number shelves driving gears all be with the sharing driving gear of two driven gear meshings, one among four driven gear of first output shaft department as idler in the middle of reversing gear. The utility model discloses a speed change gear axial length weak point, reverse gear overall arrangement and ratio coverage is wide, and parking ratchet overall arrangement wide range.