Calcium silicate whisker was prepared by dynamic hydrothermal method using analytical reagents to simulate desilication solution of coal combustion fly ash as raw material. The effects of Na2O concentration, reaction temperature, reaction time, mass ratio of alumina to silica and mass ratio of calcia to silica in the solution on phase composition and morphology of product were examined. The results revealed that calcium silicate whisker with the length over 20 mm and purity over 80% was synthesized under the conditions of Na2O concentration at 80 g/L, reaction temperature 220℃, reaction time 6 h, mass ratio of alumina to silica 0.06 and mass ratio of calcia to silica 0.9.