Asian corn borer (ACB) is distributed over East Asian and Oceania. The author analysed the main factors such as over winter population structure and envirorunental condition, metcorological condition before over winter larva pupate, meteo ralogical condition in fields on the stage of ACB emergency and hostplant. By summing up the data at home and abroad and the author’s previous research work. The author also proposed the problem existed in forecast work and made suggestions for revision.