[2] Yunnanocephalus is a small (about 2 centimetres or 0.79 inches) trilobite with an inverted elongated egg-shaped outline.

Its headshield (or cephalon) is ovate and twice as wide as long, slightly wider than and not confluent with the articulate middle part of the exoskeleton (or thorax).

The thorax has 14 segments, with short triangular spines, the 3rd and 4th slightly wider than the frontal segments, and a small tailshield (or pygidium) consisting almost fully of the axis and post axial boss, with two vaguely defined axial rings.

[3] During the ontogenetic development of Y. yunnanensis between a late larval phase (meraspis degree 9, 2½mm) and the adult (or holaspis) the facial suture changes from proparian to gonatoparian.

Usually, proparian holaspid trilobites developed from opisthoparian meraspids due to a mechanism called heterochrony.