The invention discloses a method for preparing high-quality biodiesel. The method comprises the following steps: adding a zeolite adsorbent for pre-treating cornus wilsoniana oil to obtain the pure cornus wilsoniana oil; adding pure cornus wilsoniana oil, methanol and a magnetic nano catalyst with the weight ratio of 100:15-25:0.8-1.2 in a reaction kettle for an esterification reaction; and separating a biodiesel crude product and purifying the biodiesel crude product to obtain the biodiesel According to the invention, the magnetic nano catalyst is introduced into the esterification reaction, the catalytic efficiency is high, and catalytic effect is obvious, reaction time is shortened, yield of the biodiesel is increased; the magnetic nano catalyst can be conveniently and rapidly separated and recovered according to the outer magnetic field, and enables multiple recycling. The method has the advantages of simple process, energy saving, environmental protection, short reaction time, high yield, and high product purity, and large scale and industrial production can be easily realized.