Abstract: A group of analytical formulae are obtained resently by Sun and coworkers to predict the accurate P, R, Q-branch spectral lines of rovibrational transitions for diatomic systems respectively. This study defines a contribution degree C to measure the contributions of known experimental spectral lines to the predicted line. The analyses on the predicted Q-branch emission lines of the (0, 0) band of the systems of TiF molecule show that these new formulae produce accurate values for the unknown lines of high-lying rotational states, and that the contribution degree C makes it easier for one to understand the relationships and influences among the transition lines of the given system.