The molecular formula of basic magnesium sulfate whisker is xMgSO4?yMg(OH)2?zH2O, which is a synthesized inorganic functional material with a certain aspect ratio. As a filler, basic magnesium sulfate whiskers can improve the mechanical properties such as tensile strength of the material, and also play a role of flame retardant. In the NH4+-NH3 buffer system, MgSO4?5Mg(OH)2?3H2O whiskers with length of 10 μm to 30 μm, diameter of 0.05 μm to 0.3 μm, and an aspect ratio of 30 to 150 were prepared in a one-step process at atmospheric pressure. The products were charcaterized by XRD, SEM, TG, TEM, and the influencing factors such as reaction concentration, reaction temperature, reaction time and aging time were studied combination with the characterization results. The first-principle analysis of the formation mechanism shows that the growth habit of basic magnesium sulfate whiskers accord with the dislocation spiral growth mechanism. The buffer system stabilizes the acidity and basicity of the solution and reduces the non-ideality of the reaction solution. It can make the crystals grow under unforced conditions. Basic magnesium sulfate whiskers provide an important reference for further industrial applications and the realization of low-energy-consumption production.