Abstract: A Real-time Multi-task Operator Support System （RMOSS） has been developed to support the operator’s decision making process in the control room of NPP. VxWorks, one embedded real-time operation system, is used for RMOSS software development. According to the SRK modeling analysis result of the operator’ decision making process, RMOSS is divided into five system subtasks, including Data Collection and Validation Task （DCVT）, Operation Monitor Task （OMT）, Fault Diagnostic Task （FDT）, Operation Guideline Task （OGT） and Human Machine Interface Task （HMIT）. The task test of RMOSS has been done in a real-time full scope simulator. The results showed that each task of RMOSS is capable of accomplishing their functions.