A novel double eigen angle-based steady-state flow test rig to comprehensively investigate port generated air flow inside a 4-valve EFI gasoline engine cylinder head was developed. The concept of eigenvector was introduced and the eigenvector path of the in-cylinder tumble flow was protracted; besides, the eigenvector table under different valve lifts in the dummy cylinder was shown to get a macroscopical reflection of the intensity, the tested plane, the vector direction and the distribution of the inclined swirl. In the process of the optimizing the intake system of the engine, a new methodology and comprehensive data basis were provided to organize the optimization the regional and the strength of the appropriate in-cylinder air movement, and improve the performance of the engine.