Aiming at the deficiency of existing research on the hardenability of a large module, the invention discloses a prediction method of the hardenability of a large module, which can be used for predicting the hardness distribution of the large module after being quenched by utilizing chemical composition. According to the specific scheme, the critical hardenability is calculated according to the chemical composition of steel; a calculating experiential formula is as follows: J = x1%C + x2%Mn + x3%Si + x4%Cr + x5%Mo + x6%Ni + x7%V + x8; then element parameters of the experiential formula are regressed by utilizing actual measured data of the quenching hardness of the module to obtain element parameters of a calculating formula; a hardness value of each position can be calculated by utilizing the element parameters of the calculating formula. The prediction method has the advantages that (1) the contrast between the hardness value calculated according to the element parameters of the calculating formula and each actual measured datum is not more than +/- 0.5 HRC hardness, so that the deviation of the calculated value from the actual value of the hardness is very small; (2) for the large module, the adding regularity of the elements such as Cr, Ni, Mo and V in the chemical composition of the large module can be predicted according to the thickness size of the large module.