The evaluation technology of the Attack Effect of computer networks is an important and challenging subject of security evaluation in information systems. Nowadays, corresponding theory is not mature and correlative research reports are few. In this paper several currently primary evaluation techniques of information security are concisely analyzed. Then three evaluation models, i.e., the evaluation technique based on network information entropy, the security evaluation framework based on analytical hierarchy and the synthetical evaluation technique based on analytical indexes, are presented in order to conveniently measure and estimate the attack effect. Finally, some problems which must be paid attention to in practice are pointed out.