An appropriate thermal stratification environment can be formed in impinging jet ventilation (IJV) cooling rooms. In this scenario, the well-mixing hypothesis provided by the conventional mixing ventilation is not applicable to calculate the cooling load of IJV systems. In the present study, a simple method using the cooling load ratio (CLR, α) is proposed for calculating the cooling load in the thermal stratification environment of IJV. Numerical simulations are applied to investigate the effect of several influencing factors on the CLR. Univariate analysis results indicate that the key influencing factors of α are the thermal length scale (Lm), supply airflow rate (L) and total heat gain (q*). A prediction model of α (CLR model) is developed related to the three influencing factors of Lm, L and q*. The CLR model has a high prediction accuracy in low q* situations (q* ≤ 2.5), with a slightly reduced accuracy in high q* situations. Overall, the maximum relative error of the CLR model is lower than 12%. Moreover, contour plots of α illustrate that α achieves a minimum level of 0.55, and the values of α vary between 0.55 and 1.0 for all the values of Lm, L and q*. The CLR model can provide a theoretical basis for the determination of cooling load and energy saving potential of IJV systems during the design stage.