The invention discloses a water soluble mandrel moulding method of a dipulse engine shell. The method comprises the following steps of: A, preparing a separator, a dabber and a shaft sleeve matched coaxially; B, preparing a quartz sand mixed cementing compound which comprises the following components in parts by weight: 350-450 parts of quartz sand, 9-10 parts of polyvinyl alcohol, 0.4-0.6 part of starch and 30-50 parts of water; first, mixing polyvinyl alcohol and starch to form mixed powder, then, mixing and stirring the mixed powder with water to form grume-free liquor, and finally, stirring and mixing quartz sand with the grume-free liquor; C, moulding the quartz sand mixed cementing compound as a sand sleeve; D, curing the sand sleeve; E, processing the external surface of the sand sleeve and the inner end face of the sand sleeve; F, assembling the dabber, the separator, the shaft sleeve and the sand sleeve; and G, performing surface treatment for the sand sleeve. The method disclosed by the invention is simple in moulding process, short in production period and low in cost, satisfies the design demand, and is suitable for being widely applied to the technical field of moulding solid rocket engine shells.