With the booming of airlines in the world, the “low-cost airline model” began to be more and more recognized and accepted by the general public. Low-cost airline companies rely on internal network-marketing platforms for ticket sales, which have become the main channel and method to reduce running costs. Such elements as the website’s usability, design, functionality, information and layout would affect the user experience in ordering and purchasing air tickets. The quality of website usability of the online airline booking system would have a direct influence on sales performance. Usability test conducted in this thesis aims at finding out the website usability on defects for both Spring Airlines, one of the low-cost airline companies in mainland China and AirAsia, a well-known, low-cost airline company in the world. For the Spring Airlines website, especially the simplified Chinese version, the support level for international visitors to book tickets is relatively low. The phenomenon of lag behind part of new information update and other details also lead to reduction and drop in the usability of the website. For the AirAsia website, there is improved space, such as the support level for the Chinese version of the website.