The invention discloses a method for continuous synthesis of biodiesel through a microreactor. The method is characterized by comprising the following steps of: dissolving a certain proportion of an alkaline catalyst in lower alcohol; respectively injecting the solution and grease into a continuously heated microreactor by certain proportions; reacting under a normal pressure at 40-64 DEG C; and controlling retention duration of the materials in the microreactor as 0.1-1minute, wherein the micro passage of the microreactor comprises two parts: a micro mixing passage and a micro reaction main passage. In comparison with the prior art, the process disclosed by the invention is unnecessary to additionally pre-mix the reaction materials or to use an independent micro mixer; the adopted microreactor integrates functions of mixing and reacting, and operates under normal pressure and has a simple requirement on equipment, so that mixing efficiency and reaction efficiency are further improved, retention duration is further shortened, and production intensity is greatly improved.