Some problems on Algorithmic Composition are discussed, and a survey for series of key techniques used in this approach is made, which include Markov chains, stochastic process, musical knowledge based system, musical grammar, artificial neural networks, and genetic algorithms. The conclusion is that the development of music composition system should involve a combination of the existing technologies, i.e. the Hybrid System development. In order to make the system become more practical and effective, there should be some flexible human intervenient ways for different level music composition in the system.