Monte-Carlo simulation was used to study the short-chain branch formation of polyethylene made with a Ni-diimine catalyst. Branches are formed through the chain-walking mechanism without any comonomer addition. The model describes the type of branch, that is, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octly, nonyl, and decyl (or longer branches) and the distribution of these branches in the backbone, showing information that cannot be accessed by C-13 NMR. The branching structure of these polymers seems to be determined by two major kinetic steps described by the following model parameters: a beta transfer parameter describing the ratio of monomer insertion to beta hydrogen transfer and an isomerization barrier parameter controlling the ratio among different types of branches. The model showed that methyl branches are favored on the other branches in the chain-walking mechanism. The branch distribution obtained with the model developed herein agrees well with C-13 NMR experimental results.