Chaotic characteristics analyses are conducted in a hydroelastic model test to measure the acceleration response data when different gates open due to the complexity of flow-induced vibration. First, phase space reconstruction is carried out in the measured data using average mutual information and the averaged false nearest neighbor method to calculate the optimum time delay and optimal embedding dimension. Based on these embedding parameters, the correlation dimension D2 and the largest Lyapunov exponentλ1 are calculated for each group, and the distribution law of calculation parameters is analyzed. The results show that: the lateral gate vibration is more complex than other directions, while the gate vibration complexity is more remarkable in intermediate openings; lower dimension (D2 = 3.342 ~ 5.130) chaotic attractors are present in vertical gate vibration and flow vibration, which means the vibration law of the gate along the vertical direction and flow direction can be described by fewer independent variables; and finally, λ1 of each measuring point variation with gate opening presents the trend “both sides small and the middle large”, which indicates that the vibration forecast accuracy is lower in intermediate openings.