In previous studies, rifling grooves generally ignored in simplified model of ammunition when calculating Magnus effect and rolling moment of ammunition. However, due to high requirement trajectory of small caliber ammunition, effect of rifling grooves should be studied. With the help of Fluent software, the effect of rifling groove on flow field over small caliber ammunition by comparing CFD results of smooth bullet and rifling grooves bullet. Flow fields for three different angles of attack and three different rolling rates were studied. Results show that the rolling moment and Magnus moment of the bullet smaller if the effect of rifling grooves considered. So the effect of rifling grooves should be considered in practical engineering calculation.