In present-days of giving increasingly prominence to environmental protection problems

it is neccessary to adopt a comprehensive evaluation method

which can take technical

economical and environmental factors into account

for evaluating energy and power engineering projects. The air

water

fuel and so on consumed in production （including that have been polluted） should been convrted into natural resources

the definition of final evaluation index

which is called the efficiency of natural resources

being a ratio of the energy supply production to the sum of values concerning consumed natural resources. The principle of this comprehensive evaluation method has been presented. Taking the combined cycle heat and electricity co-generation system of a preparatory natual-gas firing gas turbine unit as example

a calculation in comparison with a coal firing heat and electricity separate generation system has been roughly corried out.