The thesis concentrates on the theoretical study of the reaction of O(<3>P) withbutene. It contains two parts in this report.　　 The reaction of O(<3>P) with isobutene ((CH3)2C=CH2) is investigated using theUMP2 and CBS-4M methods. The minimum energy crossing point (MECP) betweenthe singlet and triplet potential energy surfaces is located using theNewton-Lagrange method, and it is shown that the MECP plays a key role. Thecalculational results indicate that the site selectivity of the addition of O(<3>P) to eithercarbon atom of the double bond of isobutene is weak, and the major productchannels are CH2C(O)CH3+CH3, cis/trans-CH3CHCH0+CH3, (CH3)2CCO+H2 andCH3C(CH2)2 +0H, among which (CH3)2CCO+Hz is predicted to be the energeticallymost favourable one. The complex multichannel reaction mechanisms are revealed,and the observations in several recent experiments could be rationalized based uponthe present calculations. The formation mechanisms of butenols are also discussed.　　 The mechanism of the reaction of O(<3>P) with 1-butene (C2H5C=CH2) isinvestigated based on UMP2 and G3 calculation. O(<3>P)can be added to either moreor less alkyl-substituted carbon atom of the double bond and two adducts are formed.The site selectivity of the addition of O(<3>P) is weak. From these two adducts, theintersystem crossings between singlet and triplet states could occur. The MECPs arefound using the Newton-Lagrange method, and they play a key role in the reactionmechanism. The adiabatic and non-adiabatic reaction channels including theformation mechanism of the butenols in the reaction of O(<3>P) with 1-butene arediscussed.Some calculation results are in agreement with the experimental observations.