One new genus with a new fossil species, Declinimodus setulosus gen. et sp. nov. which was found in the Middle Jurassic Jiulongshan Formation of Daohugou, Inner Mongolia, China, are described and illustrated. The new species is assigned to the Rhyacophilidae according to button-shaped of the 2nd segment of maxillary palp, and the forked R1 (in the forewing, located near apex). These new discovery are the earliest fossil records of Rhyacophilidae, which providing important evident for the study of the origin and early evolution of Trichoptera.