Computational modeling of hydrogen injection in a four stroke direct injection SI engine was investigated. The computational domain with hexahedron meshes was included the combustion chamber, intake and exhaust ports. Multidimensional principle of the fluid mechanics was used to describe the flow and physical phenomenon. The reacting flow and accompanied physical phenomena were numerically analyzed utilizing the KIVA codes. The developed model has been formulated through the finite volume method based on the structural moving grids. The grid sensitivity analysis and model validation were carried out based on the motoring condition. The developed model was successfully executed for the grid sensitivity and validation analysis. Results were presented in terms of the flow field accompanying with the gradient of hydrogen concentration. An identical hydrogen distribution was almost obtained for the low and high engine speed ranges. The vectors of the flow field were appeared to have a bigger size and coarser distribution in case of the high engine speed, especially near to the piston face. The developed model can be extended for further optimization process. © 2012 American Scientific Publishers. All rights reserved.