Aiming at the problem of early warning and evaluation of operation conditions of distribution transformers, a practical grade-warning method of operation risk in distribution area is proposed, which is based on the fusion analysis of overload rate, sustainable running time after overload and winding temperature after overload. The operating state of distribution transformer is described as the operating point of overload rate, sustainable running time and winding temperature. By analyzing the location of the operation area where the operation point belongs, the operation risk assessment of the distribution platform area is carried out, which is conducive to the operation and maintenance personnel's accurate grasp of the operating conditions of the distribution transformer in the platform area. The results of example analysis show the validity and reliability.