Abstract: Experiments were conducted in September 2016 on culture of Dendrobium primulinum in hydroponics (Hoagland) and substrate(sphagnum) for comparing their root system growth. Determinations were implemented three months later. The result showed that root system growthof water cultured D. primulinum was slower but stem growth was larger than that of substrate cultured. Light microscope of root tip, mature zone androot hair zone of the two cultured seedlings demonstrated that cortical cells of root tip from water cultured seedlings were more compact and cellinterval more smaller. The area of the pith was less in the stele of substrate cultivated and there were large starch grains. New root from the two testedseedlings was Evan blued, the result indicated that root activity of water cultured had better effect. The experiment concluded that D. primulinumcould grow well in hydroponics.