It is critical to take the fish body and fins as an integrated object to analyze the stress in the flow field which will be beneficial to conduct the research of its highly efficient swimming mechanism and bionic application. Taking carp as research objective, by the mathematical description of its body and importing the data to Fluent software to set up the model, the mechanics of the fish stressed by the flow field is conducted by the finite element method. Physical field in the calculation adopts the central difference interpolation method. Flow equation chooses standard k-ε model, then integrated with the detail parameters, the calculation is conducted. The results of the simulation indicated that the top three parts of resistance devoted in the direction of the negative x axis is the 45% of head part,29% of the fish body and 14% of pectoral fins; and also top three parts of resistance devoted in the direction of the positive y axis is the 47% of pectoral fins,29% of fish body and 14% of head part. Total force vector is (-7.88×10^-3, 2.00×10^-3,-5.87×10^-5) N. The data above show that focus should concentrated on the fish body and pectoral fins when designing the model mainly considering the lift force. The designing of fish body and head part should be focused on when mainly consider the resistance force. The simulation result provides a sound mechanics foundation for the future research of controlling of the bionic robot fish.