A double eigen angle steady-state flow rig was used to measure three modified options of intake port on a single cylinder four stroke gasoline engine. The results showed that improving combustion by enhancing swirl might reduce the flow capacity while improving tumble ratio appropriately could also increase the intake flow coefficient. Based on the dimensionless swirl ratio and tumble ratio, a group of simple formulas which were used to calculate the inclined swirl characteristic parameters were proposed, and related experiments were accomplished to prove their effectiveness. Additionally, linear regression analysis was conducted between the dimensionless swirl ratio at the condition characteristic angle α of 60° and the dimensionless inclined swirl ratio synthesized by swirl ratio and tumble ratio, and the correlation coefficient of three options were 0.96, 0.97 and 0.97 respectively. It was concluded that the performance of intake port could be evaluated by the dimensionless swirl ratio at a certain angle α instead of swirl ratio and tumble ratio.