The　nonlinear　resonance　problem　of　composite　lattice　sandwich　panels　is　studied　when　both　1:　3　internal　resonance　and　external　combined　resonance　occur　simultaneously.　Firstly,　based　on　Hamiltonian　principle　and　layered　displacement　field　theory,　the　vibration　partial　differential　equation　of　composite　sandwich　panels　was　established.　Then,　the　ordinary　differential　equation　obtained　by　Galerkin　discretization　was　solved　using　multi-scale　method,　and　the　modulation　equation　of　the　sandwich　panel　was　obtained　in　the　presence　of　both　internal　and　combination　resonances.　Finally,　the　bifurcation　diagram　of　the　steady-state　equilibrium　solution　of　the　modulation　equation　with　changes　in　system　parameters　was　obtained　using　numerical　methods.　The　effects　of　different　lattice　core　cell　configurations,　external　excitation　frequencies,　and　external　excitation　amplitudes　on　the　nonlinear　combined　resonance　characteristics　of　composite　lattice　sandwich　panels　is　studied.　©　2024　Journal　of　Dynamics　and　Control.　All　rights　reserved.