The invention relates to an air brick fired at low temperature by using a gel and a preparation process of the air brick. The raw materials of the air brick include an aggregate and a fine powder, wherein the weight ratio of the aggregate to the fine powder is 6.5:3.5-7:3; the alumina gel fine powder is used as a binding agent; due to the addition of the alumina gel particle having quite high chemical activity into the air brick in the firing process of the air brick at the temperature being lower than 800 DEG C, the air brick body has high strength; the addition of chromium sesquioxide fine powder can effectively improve the capacities of resisting the permeability of molten steel and the erosion by the steel slag in the use process of the air brick, so as to ensure the good application performance of the air brick; and the firing temperature of the air brick provided by the invention is controlled at 500-800 DEG C, but the firing temperature of a traditional air brick is generally higher than 1300 DEG C, and therefore, the cost of the fuel gas can be saved by about 60% and the firing time can be shortened by about 50%.