The invention discloses a method for acquiring random fluctuation information of tie-line power. The method comprises steps as follows: 1), load levels P1 and P2 of connected two-side electrical power systems are acquired, wherein the two-side electrical power systems constitute an interconnected electric power system, and a mean square error c of load deviation mean values of the interconnected electric power system is calculated according to the load levels P1 and P2 of the connected two-side electrical power systems; 2), generating capacity P1H and P2H of the connected two-side electrical power systems is acquired, then a mean square error Rho of tie-line power fluctuation of the interconnected electric power system is acquired according to the mean square error c of the load deviation mean values of the interconnected electric power system and the generating capacity P1H and P2H of the connected two-side electrical power systems, and the random fluctuation information of tie-line power is acquired according to the mean square error Rho of tie-line power fluctuation of the interconnected electric power system. By the aid of the method, the random fluctuation information of tie-line power of the interconnected electric power system can be accurately acquired.