This paper studied the potential mechanism of form drag from emergent vegetation by the effective combination of experimental verification and numerical simulation. The rigid cylindrical sticks arranged in the open channel were used to simulate vegetation and experiments on flow velocity distribution characteristics in open channel with different vegetation density and vegetation arrangement forms were carried out. Based on the new expression of hydraulic radius from the recent paper, it indicates the form drag from vegetation is closely related with the wake volume near the vegetation. The relationship between the wake volume and form drag is proposed and verified by different experimental conditions. Based on this relationship, the experimental results show that the resistance form of vegetation in vegetated open channels can be divided into: K-type and D-type based on different sticks arrangement within one vegetation patch. The calculated values and measured values achieve a good agreement under different experimental conditions. Meanwhile, numerical simulation based on SAS turbulence model was conducted and the simulation results also fit well with the experimental values so more complex experimental conditions are simulated by numerical simulation method. The results of this study will provide a theoretical basis for the layout of vegetation in the ecological open channel.