The invention provides a safety and stability control system online strategy constant value checking method; an off-line strategy is formulated under the consideration of the operation mode by an operator, however, when the actual power grid encounters certain extreme operation modes, failure of the off-line voltage stabilization strategy is caused; the off-line strategy is made based on certain specific faults, and if some multiple successive faults occur in the power grid, a strategy table is caused to be mismatched, and the power grid suffers from a instability risk; the off-line strategy is not an optimal value for some operation modes, and over-cutting and poor economic performance in actual operation are caused; and the off-line strategy making work is complex, so that an operator which is rich in experience is needed in analysis, gathering and classification processes, and the operator faces great challenges. According to the method, the online strategy constant value is checkedfor many times from different aspects, so that the reliability of using the online strategy constant value of the stable control system is improved, and a technical guarantee is provided for safe andstable operation of the power grid.