The invention discloses a safety check and assessment method used for a multi-cycle power generation transmission transformation repair plan. The method comprises the steps of automatically judging a calculation cycle according to a time span of the repair plan; selecting a calculation time point; generating a calculation time period set; integrating prediction data, plan data and historical data to generate a future cross section; calculating alternating-current power flow distribution; realizing safety check, SCED and unit combination adjustment closed-loop iteration processes; performing ground state check analysis and N-1 check analysis on the power flow of the future cross section; when the check is not passed, adjusting an output of a unit by utilizing an SCED model; when the SCED model does not have a feasible solution, adjusting a unit combination; then performing safety check again; and finally, comprehensively assessing the influence of equipment repair on power grid safety through comparative analysis of a ground state power flow change before and after repair, a power flow change before and after N-1 connection and disconnection, and a power flow change, before and after N-1 connection and disconnection, of equipment with a relatively great change before and after repair. Therefore, the equipment repair risk is lowered and the power grid safety level is improved.