The investigation showed that red core wood of poplars was the result of the physiological action of trees that played a key role and the infection by bacterium and fungus by investigating in the forest field. By separating, inoculating pathogens and control test in both laboratory and field, core stain should occur if only poplars were damaged. It should aggravate core stain if poplars were inoculated by relative fungus and bacterium in cut. The result of chemical prevention tests was not very effective.