Material. Holotype: male, China, Yunnan, Tengchong, Zhengding, 1800m, 15 -VIII- 2006, Xin Yu leg. Holotype will be deposited at Institute of Entomology, Life Sciences College of Nankai University, Tianjin, China.
Etymology. Named after the name of type locality.
Description. Male. Labium pale white. Labrum, bases of mandibles, genae, anteclypeus and frons blue; base of labrum and whole postclypeus black; top of head including antennae black, postocular spots blue, almost circular; postoccipital stripe absent. Prothorax black dorsally, blue laterally ( Fig. 18). Synthorax black dorsally, with narrow blue antehumeral stripes. Sides of synthorax blue, with a black stripe along second lateral suture ( Figs. 10, 12). Legs pale blue with extensor surfaces of femora, flexor surfaces of tibiae, tarsi and claws black. Wings hyaline, pterostigmata brown, braced, each covering one cell. Abdomen blue with black as follows: segment 1 with a big basal dorsal mark and short lateral stripes, segment 2 ventrally and with a rectangular dorsal mark subdistally, long lateral stripes, and distal annulus ( Fig. 12); segment 3 black ventrally and distally, with a small spot dorsally; laterally along segment 4 and apical one fourth dorsally; segments 5 and 6; segment 7 ventrally, as well as distal 0.30 dorsally and 0.50 laterally ( Figs. 10–11); segments 8 and 9 almost blue except for short lateral stripes on sides of segment 8; segment 10 black. Caudal appendages ( Figs. 13–15) black; cercus as long as paraproct, both a little shorter than segment 10. Genital ligula ( Figs. 16–17) with shield-like head and flagella.
Measurements (mm): abdomen + appendages 27. 0; hind wing 19. 0.
Diagnosis. This new species is similar to C. hylas in coloration pattern and caudal appendage structure, but the genital ligula of C. hylas has no flagella and lacks black on the ventral surface of synthorax. The type locality for C. tengchongensis also includes C. dorothea but they can be separated from each other easily by body coloration pattern, and caudal appendage morphology; the cercus of C. dorothea is longer than the paraproct. Coenagrion tengchongensis differs from C. aculeatum by lacking the short spine-like lateral lobes on the genital ligula.