The invention discloses methods and systems for evaluating and diagnosing energy efficiency of energy consuming equipment. The methods includes determining an evaluation index group according to equipment type of the energy consuming equipment, and based on related data of the energy efficiency of the energy consuming equipment, calculating value of each energy efficiency evaluating index in the evaluating index group by adopting mathematical calculation models of the energy efficiency evaluating indexes; acquiring at least one level of energy efficiency evaluation reference value of each energy efficiency evaluation index from an energy efficiency benchmarking base; comparing the value of the energy efficiency evaluating index with the energy efficiency evaluation reference value of each level, and determining a benchmarking result of the energy efficiency evaluation index according to a comparative result; and acquiring an energy efficiency evaluation result of the energy consuming equipment by adopting an evaluation rule corresponding to the equipment type to the benchmarking result of each energy efficiency evaluation index. By the system, reliability of energy efficiency evaluating and diagnosing can be improved.