A coding method and system with an adaptive bitplane coding mode is provided to code multiple bitplanes of a frame consisting of multiple macroblocks. Each bitplane consists of macroblock modes used by the macroblocks of the frame. The method includes the steps of: (A) initializing a bitplane coding mode of the frame as a compress mode; (B) coding the frame and the bitplanes to thereby obtain coded bitplanes, and calculating the bit number of coded bitplanes; (C) calculating the bit number of uncoded bitplanes; (D) executing step (A) when the bit number of coded bitplanes is smaller than the bit number of uncoded bitplanes; (E) initializing the bitplane coding mode of the frame as a raw mode when the bit number of coded bitplanes is not smaller than the bit number of uncoded bitplanes.