Tripartite entanglement dynamics is studied in terms of a generalized negativity for two kinds of mixed states in the Tavis-Cummings model with intrinsic decoherence, where the arithmetic and geometric mean negativities, which have been widely used to three qubits in recent literature, are included for consistency and comparison. Analytical and numerical simulations for various states in the model without and with intrinsic decoherence as well as without rotating-wave approximation show that the dynamical correlations between those negativities are dominantly positive when the field is initially prepared in the states with more than two photons. Such correlation between the arithmetic and geometric mean negativities is positive for a suitable state. The dependence of the steady-state entanglement on initial conditions demonstrates that the generalized negativity and the arithmetic mean negativity behave in a similar way. Moreover, a hierarchy of those indicators in entanglement dynamics and the steady-state entanglement is the same for various parameters in the model and initial states. Those are useful for tripartite entanglement and quantum information.