The present invention relates to a CaSO4 crystal whisker with desulfurized gypsum as raw material and a preparing method. A technical scheme includes: mixing desulfurized gypsum, water and habit modifier fully for forming suspension; wherein, mass concentration of desulfurized gypsum is 1-8%, mass concentration of habit modifier is 5-20%; or stirring the above suspension 1-3 hours under conditions of normal pressure, 100-128 deg c and 120-210 r / min stirring speed, adding calcium sulphate crystal whisker by weight of 0.5-1% as inoculating crystal, reacting 1-3 hours, adding modifying agent, or stirring the above suspension 3-8 hours, adding the modifying agent directly; or stirring the above suspension 3-8 hours, and adding the modifying agent directly, the amount of the modifying agent is 0.4-1% of the suspension weight, stirring 0.5-1 hours; then pump filtering, washing and three-section drying for obtaining three various type calcium sulphate crystal whisker. The method uses a normal pressure salt solution crystallization method for preparing CaSO4 crystal whisker which has short process flow, geniality condition and low cost, and is an efficient purpose for realizing resource utilizing.