Laboratory tests had been conducted on the helical strakes of the riser, the aim of the present work is to further improve the understanding of the response performance of VIV for the riser with helical strakes. The experiment was accomplished in the towing tank and the relative current was simulated by towing the flexible riser in one direction. Based on the modal analysis method, the displacement responses can be obtained by the measured strain. The strakes with different pitches were analyzed here, and the response parameters like strain response and displacement response were studied. The analysis has indicated that the in-line response is as important as the cross-flow response. The results also show that the response characteristics of a bare riser can be quite distinct from that of a riser with helical strakes, and the response performance is depend on the geometry on the helical strakes closely.