Anhydrous calcium sulfate whiskers (CSW) were prepared by hydrothermal method using ammonium sulfate wastewater as raw material. The influences of sodium dodecylbenzene sulfonate (SDBS) and polyethylene glycol (PEG) with varying polymerization degrees on growth behavior of CSW were researched. Additionally, the molecular dynamics simulation of SDBS adsorption on the surface of CSW using Materials Studio 2020 software was simulated and the adsorption energy of each crystal plane was calculated. The results show that all products belong to CSW of orthogonal crystal system. CSW prepared without additives has an average length of 65.27 μm and an aspect ratio of 40. However, the surface is rough and the distribution is uneven. On the other hand, the CSW prepared by adding 4% (mass fraction) SDBS has the best morphology, uniform distribution, smooth, and needle-like surface, with an average length of 136 μm and an aspect ratio of 62. SDBS promotes the axial growth of CSW in the form of spiral dislocation, so that the aspect ratio of CSW is refined.