The concept of computer network application reliability was introduced, and it focuses on the different reliabilities caused by different applications. On the basis of the index evaluation method, the testing procedure of local area network(LAN) file transfer protocol(FTP) application reliability was discussed and a novel testing and evaluation method was proposed. Meanwhile, an LAN in a laboratory was tested and evaluated by the method mentioned above. In this case, to solve those problems in the testing process, a Windows batch script to generate FTP packets was programmed as the LAN application traffic generator; a testing data collection method was studied on based on Sniffer Pro. And also, the testing steps were given and the reliability evaluation results were attained. In the testing case, the collected data matches with the network state. Therefrom, the proposed testing and evaluation technology is verified and can be seen as a reference provided for other application reliability study.