Abstract: A 50 L bioreactor with multi-parameter monitoring and control function was employed in this paper to analyze the metabolic characteristics of cephalosporin C fermentation.It was shown that strain morphological differentiation at early stage was favourable for the increase of dissolved oxygen,and the formation of swollen and fragmented mycelium could initiate cephalosporin C synthesis. Soybean oil fed in the middle phase of fermentation was used as carbon source and anti-foam agent,whereas in the late phase of fermentation it served only as antifoam agent.The dissolved oxygen regulation strategy was proposed according to the association analysis of multi-parameters.