The invention relates to a controller applied to a multiphase motor speed adjusting system. The controller comprises a bus board, a power source board card, a main processor board card, an analog quantity conditioning board card, a switch quantity input and output board card, an optical fiber driving board card and a communication through-connection board card, wherein the power source board card provides various power sources to all the other board cards through the bus board, driving and feedback signals of the optical fiber driving board card, a switch quantity signal of the switch quantity input and output board card, an analog quantity signal of the analogy quantity conditioning board card, a communication signal of the communication through-connection board card perform information interaction with the main processor board card through the bus board, and the communication through-connection board card and the main processor board card respectively at least have communication with an upper computer. The controller has the advantages of being high in modularization degree, having flexible expandability, being capable of not only controlling the complex multiphase motor speed adjusting system in real time, but also greatly enhancing the expanding flexibility due to the fact the bus board is deigned in a bus mode, and being capable of effectively controlling development cost, shortening the development period and meanwhile improving equipment reliability.