Given that the attacker has the side information of adaptivity criterion

it is an urgent problem for the steganographer to improve the security of large-payload and adaptive steganography.This paper proposed a game-theoretic model for the two sides.Through theoretical derivation

we provided the necessary conditions for game equilibrium

along with the mixed strategies and expected payoffs of the two sides in equilibrium.Results of numerical simulation validated the theoretical analysis.This research reveals that the attacker's strategy is independent of the number of hidden bits

and the expected payoff increases with the number of hidden bits.The probability that one position is selected by steganographer to embed more bits is always greater than zero and increases with the complexity of that position.These conclusions bring some guidance for devising secure adaptive steganography with large payload.