When analog quantity control is realized by using DCS, the division of subsystems shall follow the independent complete principle, thus minimizing the information exchange capacity of the data communication bus. During task allocating to DCS control station, the following principles shall be met. Module fault will not cause the unit to trip, and the unit can shut down safely when DCS control station is in failure. The controller modules for fulfilling the analog control shall be redundantly configured; the important signals shall be input from different input modules. The control system shall not form a closed loop control circuit, through the data communication bus because there is uncertainty in data transfer time of communication bus, which changes the dynamic characteristic of the control object, thus making the control quality difficult to guarantee. The maximum execution cycle for the processor module of controlled by analog quantity to fulfill all the tasks given shall not exceed 250 ms, the execution cycle of processor controlled by switch quantity shall not exceed 100 ms. For fast processing simulation and sequential control circuit, the processing capacity shall be respectively be performed once every 125 ms and every 50 ms respectively.