The calculation of rate constants of addition and abstraction reactions of 2,4,4-trimethyl-l-pentene with H and O(P-3) were conducted by conventional transition state theory (TST) and canonical variational transition state theory (CVT). Potential energy surfaces of reactions were calculated at the DLPNO CCSD(T)/cc-pVTZ//M06-2X/6-311G(d,p) as well as the CCSD(T)/6-311++G(d,p)//M06-2X/6-311(d,p) level. Moreover, quantum mechanical effects were determined by multidimensional small-curvature tunneling (SCT) and zero-curvature tunneling (ZCT) methods. 2,4,4-Trimethyl-l-pentene contains primary and secondary allylic, alkylic, and vinylic H atoms. It also contains addition reactions into central and terminal carbon atom channels. The results indicated that allylic H abstraction channels dominate the overall H abstractions resulting from the lower barriers. In addition, a radical added into terminal carbon dominates the addition reactions. The branching ratio is more than 72% above 1500 K for H abstraction and more than 90% below 500 K for H addition reactions.