The invention provides a device and method for preparing biodiesel through a rotary fixed bed fast reaction. The device is mainly composed of a fixed bed reactor with a rotary shaft (9). Firstly, the fixed bed reactor filled with a solid catalyst is added to reactant methyl alcohol, and meanwhile a motor (12) is started to enable a reaction still to rotate. The dropping speed of raw material oil is controlled, and the oil and excessive methyl alcohol are subjected to the fast reaction. The contact chance of the reactant and the catalyst can be increased through rotating, more active point locations can be occupied, and sinking and separation of fatty acid methyl ester can be promoted. By means of a liquid redistributor, the phenomenon that liquid is unevenly distributed due to rotary centrifugation is avoided. The layering condition of sight glass (21) is observed, and products are removed in time. A forward reversible reaction can be accelerated through excessive methyl alcohol, timely removal of the products and the rotary reaction still. The advantages of being easy to operate, high in raw material utilization rate, high in esterification efficiency and the like are achieved, and the device and method can be used for fast and continuous preparation of the biodiesel.