n order to establish a dynamics model of the diamond jointedwing configuration UAV, a dynamics modeling method based on Lagrange’s equation is proposed. Firstly, the quaternion is selected to parameterize the attitude of the UAV, and the constraint matrix of the UAV system is established. Secondly, a generalized force matrix of the UAV is established by the virtual work, the Kinetic and Potential energy of the UAV are established. Finally, a matrix is obtained by the concept of matrix direct product and the product of this matrix and the constraint matrix is a zero matrix. The Lagrange multipliers in the Lagrange’s equation are eliminated by the matrix, and the dynamics model of the UAV is established in modularization based on the Lagrange’s equation. In order to compare with the Lagrange’s equation, the Kane equation and ADAMS software are also used to establish a dynamics model of the UAV. The results show that the simulation of Lagrange’s equation, Kane equation and ADAMS software are basically the same, and the rationality of the dynamics modeling in this paper is verified.