With the rapid development of society, technology and economy, the economic circumstance in China has undergone great changes, for it has entered into a world with more intense competition. The development and application of computer in economic field has led to major changes in the world economic system. Computer technology, contributing a lot for the rapid growth of China's economy, gains the most rapid development with the most beneficial economic structure since China's reform and opening up. Now, computers occupies a very important position in all walks of life, and have changed the operating mode of modern enterprises, such as the company information storage, transmission, data analysis etc., greatly improving the efficiency of enterprises, increasing the global competition of enterprises. However, there follows the network security issue with the application of computer, how to ensure the safety of the internal data in modern enterprise is the foremost issue. This study analyses the current status of application of computer network system in the modern enterprise, introduces the application of various computer network technologies in enterprise and network security issues, and the way to ensure corporate computer network security, such as the protection of transferred data from malicious tampering, deletion, theft, etc. Only with the establishment of a healthy and harmonious enterprise network environment can the development of modern enterprise get promoted. And the insurance of security technology in modern enterprisesÂ computer network will provide staffs more professional, complete service, with a rather high feasibility and reliability. Thus not only can the development goals of modern enterprise network security system be achieved, the effectiveness of modern enterprises can be largely promoted too.