Abstract: Under the background of the engineering project for Shougang 2160 hot strip mill, the digital vector control system of a cyclo converter-fed synchronous motor drive was investigated. The composition and main technical characteristics of main circuit and control system were expounded, and especially thyristor trigger and speed control researched. The speed control system with load observer was developed to solve poor dynamic character of load fluctuate. The research results have been used on site, the precision of speed control is better than 0.01%, and the dynamic respond time is less than 50 ms.