The invention discloses a formula and preparation method of an iron ore concentrate pellet bentonite bonding agent, and belongs to the technical field of iron and steel industry pellet production. Theproblem that the cost of bentonite for iron ore concentrate pellets is high is solved. The bonding agent is composed of 45%-50% of bentonite powder and 50%-55% of calcium oxide powder; the bentonitepowder contains 1%-5% of CaO, 15%-20% of Al2O3 and 60%-65% of SiO2; the particle size of the bentonite powder and the calcium oxide powder is -0.074 mm and accounts for 90%-95%; and it is guaranteed that the CaO content of the mixed bentonite bonding agent reaches 45%-55%. The preparation method comprises the steps that firstly, the CaO content and the particle size of the bentonite are inspected;and secondly, the proportion of the calcium oxide powder accounting for 98% of the CaO content is determined according to calculation of the actually-detected CaO content, and the CaO content of thebentonite bonding agent obtained after batching and uniform mixing reaches 45%-55%. According to the formula and preparation method of the iron ore concentrate pellet bentonite bonding agent, a new way for reducing the cost is explored for the current meager profit and operating loss conditions of iron and steel enterprises.