The invention provides a computer simulation method and system based on a power grid. The computer simulation method comprises the steps of obtaining network nodes and corresponding elements of the power grid; generating a topology structure of the power grid; conducting characteristic extraction on the network nodes and the corresponding elements in the topology structure; determining the networknodes and the corresponding elements which causes that the probability of outage events is larger than a preset threshold value; generating a set of the network nodes and the corresponding elements which causes that the probability of the outage events is larger than the preset threshold value; conducting outage event simulation on the set; determining whether the outage events occur or not according to the result of the simulation; if yes, adopting an emergency prearranged plan and diagnosing the network nodes and the corresponding elements causing the outage events; if not, determining whether to repeat the steps or not according to conditions. By means of the computer simulation method and system based on the power grid, the simulation result can be more accurate, the probability of the occurrence of the outage event is further lowered, the waste of power after the outage events inevitably occur is reduced, and the harm brought after the outage event occurs is lowered.