Operation of grid enterprise has the following specialities:large investment, long operating circle,limited price of supplying eletricity and high requirment to security. Under these limited conditions,to improve technical economic value of grid investment and get reasonable returns,enterprisesmust evaluate investment benefit by to scientific evaluation method. The paper probes mathematics evaluation on investment returns of grid,discusses such matters assimple methods of index, normalized treatment and weight calculation,and gets synthetic methematics model of evaluating general grid investment returns. This evaluation method applies to every stage or whole life circle of long period grid investment.