This paper suggests a method to synthesize a long background music sequence from a given short music clip in real-time. The copies of input clip are placed with overlapped region, the length of which is computed by random or clip matching method. Based on pitch, rhythm and chord cut criteria, the cutting point of the two clips is computed within the overlapped region. As a result, the two clips are concatenated at the cutting point. Generating some variations such as mirroring, retrograding and transposing of the given music clip makes the synthesized result much more dynamic. Suggested method is especially useful for interactive and real-time applications such as games and web contents.