The effect of pressure, temperature and time of secondary grads crystallization on the purity and the crystal ratio of andrographolide were investigated via single factor experiments, observing shape of crystal with scanning electron microscopy(SEM), determining purity of andrographolide by high pressure liquid chromatography(HPLC). The result showed that the particle of andrographolide was much maller, moreover, the crystal of andrographolide was distributed in floccule on crystallization board; When the optimized parameters(pressure 14 MPa, temperature 55℃, time 60 min) were selected the content of andrographolide was more than 90%, the crystal ratio was more than 45%.