Density functional calculations have been used to study the mechanism of 1-phenyl-1-(3-pyridyl)ethene hydroformylation using rhodium catalyst. Our calculations reveal that the rate-determining step is the oxidative addition of hydrogen molecule and the preferred path is the one involving ts3ans for the lowest activation free-energy (△rGa), 63.8 kJ/mol. This reaction is demonstrated to be strong exothermic by -96.6 kJ/mol of branched products and -98.2 kJ/mol of linear products. And the predominant product is the linear 3-phenyl-3-(3-pyridal)propanal (pr-ns) determined by both thermodynamics and kinetics. These results are in agreement with the practicality experimental studies.