When water flows through the caisson，the caisson’s compression across the water section will change the flow field around it. To explore the change of stress on the caisson under different velocities，flow，and caisson depths，we adopt the control variable method to study the flow field variation law in the process of caisson bedding and floatation based on the model experiment and CFD numerical simulation. In view of the shortcomings of the standard formula for large structure calculation，we propose the lateral compression coefficient for modification. The calculation results show that with the increase of the flow velocity，the flow force and flow velocity distribute in a parabolic curve；with the increase of the flow direction angle，the longitudinal flow force and transverse flow force of the caisson increase simultaneously；during the gradual uplift of the caisson，the flow increases at first and then decreases；when the distance between the bottom of the open caisson and the riverbed is more than 10 m，the flow force of the open caisson will remain stable regardless of the water depth.