Disclosed are a method and an apparatus for realizing signal to noise ratio (SNR) scalability in a video stream server in order to transmit a video stream in a variable network environment. An apparatus for adapting a bitrate of a coded scalable bit-stream based on multi-layers to a variable network environment, comprising a bit-stream parsing unit to parse an input bit-stream, a pre-decoding condition determining unit to determine a target transmission bitrate according to the variable network environment, a pre-decoding unit to skip at least one frame among the frames included in the parsed bit-stream according to the determined target transmission bitrate, and a bit-stream transmission unit to transmit to a client device the bit-stream that has been restructured due to frame skipping.