The invention discloses functionalized alkaline ionic liquid and the application thereof in the preparation of biodiesel. By using vegetable oil and methanol as raw materials, the biodiesel is obtained through heating reflux under normal pressure. Compared with the prior art, the functionalized alkaline ionic liquid has the advantages that (1) by adopting the functionalized alkaline ionic liquid,the source of raw materials is wide and the preparation is facilitated; the activity of a catalyst is high and the use amount of the catalyst is small; (2) the reaction condition is mild, and a reaction can be conducted at a temperature slightly higher than the normal temperature, so that both environmental benefits and economic benefits are gained; (3) the raw materials do not need to be pretreated, so that equipment investment is reduced and the process flow is simplified; and (4) the catalyst has excellent thermal stability, can keep steady performance during either a reaction process or post-treatment, can be circularly used and is environmentally friendly.