The present invention relates to an audio synthesis system for performing wavetable audio synthesis. The system comprises an instrument database, an analysis module, a memory, a judgment module, and a synthesis module. The instrument database is used for storing data of a first predetermined number of musical instruments. The analysis module is used for analyzing an inputted wavetable music to generate required data of a second predetermined number of musical instruments. The memory has a predetermined capacity for storing the required data of musical instruments to synthesize the wavetable music. The judgment module is used for judging whether the total amount of data of the second predetermined number of musical instruments exceeds the predetermined capacity. The synthesis module is used for synthesizing a digital music signal according to the instrument data stored in the memory.