An embodiment of this invention discloses a network game anti-cheating device, method and system. The device includes: an information processing unit, adapted to modify actual game state information to dummy game state information, and send the dummy game state information to a terminal of a player; and a seat assignation unit, adapted to assign a player into an unoccupied seat of an idle table according to actual table information in a game room. The information processing unit comprises: a table information processing unit, adapted to send dummy table information in the game room to the terminal of the player; a watching information processing unit, adapted to send dummy game information of players who are playing the game on the table; and a partner-player information processing unit, adapted to send dummy information of the partner-players on the table.