Visualization technique was adopted to study influence of intake air velocity on fuel injection. Results showed that evaporation of fuel could be promoted by increasing velocity of intake air. Influence of intake air on evaporation of spray was different if spray angle was changed. For the engine used in study, more fuel can enter cylinder directly if fuel was injected on the back of intake valve and inlet. With increasing distance of fuel injection, front end area of spray increased and more fuel would enter cylinder directly. Evaporation of spray can be promoted by high temperature back flow. Fuel injected before intake stroke would reflect against the inlet and intake valve, evaporation of reflected fuel could be promoted by intake air.