The genus was named in 2006 by Wang Li, Li Li, Duan Ye and Cheng Shao-li. The genus name is derived from the old name of Chaoyang City, Longcheng, and a Latinised Greek pteron, "wing". The specific name honours Zhao Dayu, the president of Shenyang Normal University and a contributor to the founding of the Western Liaoning Institute of Mesozoic Paleontology.
Longchengpterus is based on holotype LPM 00023, found at Yuanjiawa near Dapingfanga, a compressed incomplete skeleton and partial skull on a single plate. The posterior part of the skull has been damaged. It is elongated with a length of 262 millimetres. The large skull opening, the fenestra nasantorbitalis, is triangular in form and occupies much of the snout. The teeth in the upper jaw are concentrated in the front part and spaced far apart; their number is uncertain. The lower jaws have been well preserved. They are 220 millimetres long and their symphysis is short. Twelve teeth are present in the dentary. They have a sharp point but are laterally compressed, curving slightly inwards.
The humerus, 88 millimetres long, has a low deltopectoral crest and no pneumatic foramen. The fourth metacarpal is longer than the first phalanx of the wing finger. The wingspan was about two metres. The pelvis has been heavily damaged. Part of a femur is present, its estimated length was 91 millimetres.
Longchengpterus has been assigned to the Istiodactylidae sharing with Istiodactylus tooth form and count as well as a large skull opening. A notable difference is the lack of a broad snout. It was the second istiodactylid named and the first from China, adding to the known pterosaur diversity from Early Cretaceous layers of China.