This thesis takes top tensioned vertical riser interaction as its main study object. It has its focus on the understanding of the mechanism about potential instability of the risers caused by the interaction and the prediction of potential collision. Started from two-dimensional cylinder interaction cases, and later extended into the three-dimensional riser scenarios, the problem is investigated comprehensively. The study covers fluid force prediction, stability analysis, continuation investigation and dynamics simulation. The study disclosed the mechanism of the potential collision when the flow velocity reaches a certain critical value, and provides a robust tool to predict the threshold for the riser collision. Additionally, the investigation shows the difference between marine riser interaction and the similar interaction occurs in other engineering disciplines, such as power transmission lines, heat exchangers etc. Also provided in this thesis are valuable information regarding the riser dynamics should collision occur. The research will be beneficial to the marine riser designers and operators.