The invention particularly relates to a chromium-free basic brick for a cement kiln and a preparation method thereof. The preparation method adopts the technical proposal that: firstly, mixing 45 to 96 weight percent of magnesia, 2 to 17 weight percent of Al2O3, 1 to 10 weight percent of iron, 0 to 40 weight percent of hercynite or magnesium aluminate spinel and 0 to 10 weight percent of Fe2O3, and adding a water glass solution or a sodium tripolyphosphate solution or a sodium hexametaphosphate solution which is 3 to 6 weight percent of mixed materials; and secondly, performing mixing, forming, roasting and hardening treatment. The preparation method utilizes a high-temperature environment at a temperature of 1,500 DEG C when products are used to generate the hercynite through in-site chemical reaction in the service process of unfired bricks, so that the chromium-free basic brick for the cement kiln has the superior characteristics of periclase-hercynite bricks. The preparation technology is simple, does not require high-temperature firing, and saves energy resources; and metallic combination is formed in green bricks through plastic phase transition of metallic phases under the action of forming pressure, and has the function of reinforcing and plasticizing the green bricks, so that the green bricks have large volume density, high strength and good thermal shock stability.