Computer -monitoring system on the fixed bed reactor in small -scale hydrogenation unit was introduced .In the process of chemical production, fixed bed reactor heater temperature control system by the centralized collection was illustrated .Sampling control algorithm and the outputs way of the adjustable pulsing width were used to control the reactor heater temperature of greater with pure hysteretic characteristics .The process flow , scheme of temperature control , the function of system and the functions of hardwires , the design of software and the control algorithm were discussed.After two years' continuous operation , automatic control is realized on the bench scale hydrogenation unit with computer -monitoring system .The analysis of product show that the conversion of toluene is 24.3% (expected 16 %).Methyl alcohol conversion is 100 % and the expected indication of quality is obtained .