Cleistocactus parviflorus grows as a shrub with upright, green shoots that are slightly branched at the base and reaches heights of up to 3 meters with diameters of up to 4 centimeters. There are 12 to 15 clearly notched ribs. The different colored spines are brown to yellowish to greenish. The 1 to 3 central spines are thicker and yellow up to 2.5 centimeters long, the 5 to 9 radial spines are up to 4 millimeters long. The straight, red flowers are 2.5 to 3.5 centimeters long, 8 millimeter wide, red and yellow, with purple tepals. The yellow fruits are up to 1 centimeter in diameter.
The first description as Cereus parviflorus was made in 1897 by Karl Moritz Schumann. The specific epithet 'parviflorus' is derived from the Latin words parvus for 'small' and -florus for '-flowered'. Robert Roland-Gosselin placed the species in the genus Cleistocactus in 1904. A nomenclature synonym is Echinopsis parviflora Anceschi & Magli.