In our previous experimental study [Chem. Phys. Lett. 179 (1991) 442], three propensity rules of rotational energy transfer on CO (e(3)Sigma(-), v = 1) collision with He were obtained experimentally. To interpret these propensity rules theoretically, a theoretical model is presented in this Letter, based on the time-dependent first-order Born approximation. Not only three propensity rules, which obtained experimentally, are interpreted theoretically, but also a new propensity, which is not concerned in the experiment, is also derived theoretically. (C) 2003 Elsevier B.V. All rights reserved.