The invention discloses a preparation method of a fuel. The preparation method is characterized by comprising mixing sludge, cassava dry grains, quicklime and high temperature-resistant aerobic bacteria uniformly, performing stacking fermentation on the obtained mixture until water content in the mixture is reduced to below 40 weight%, wherein the additional amount of the cassava dry grains is 30-60% weight% and the additional amount of the quicklime is 2-10 weight%, based on the weight of the sludge; the additional amount of the high temperature-resistant aerobic bacteria is 0.125-0.25 billion based on every kilogram cassava dry grain; the high temperature-resistant aerobic bacteria can at least endure a temperature of 50 DEG C. The invention also provides a fuel prepared by the above method. The preparation method of the fuel provided by the invention and the fuel prepared by the method solve the difficult problem of sludge resource utilization and have wide application prospects and significant economic benefits and social benefits.