In this paper, we derive a rigorous expression of the nuclear gradient using the QED Hamiltonian without making unnecessary approximations (such as the RWA). We treat the molecule-cavity hybrid system as a MQC system, where the electronic-photonic DOFs are treated quantum mechanically, and the nuclear DOFs are treated classically. Using the electronic adiabatic states for the electronic DOF and the Fock basis for the photonic DOF, and requiring the total energy conservation of this MQC system, we derive the rigorous nuclear gradient, and it is intuitively connected to those approximate gradients under the JC approximation. Our gradient expressions, and the corresponding MQC scheme, can in principle include any number of electronic states and photon number states which is a desired property for investigating the dynamical process of polariton chemistry. The nuclear gradient expression can be readily used in any MQC simulations, such as Ehrenfest and FSSH approaches demonstrated in the result section.