Large Telescope Control System (TCS) is a complicated system, which contains thousands of actuators. Wired TCS is inconvenient to point and track for a large telescope. This paper proposes a TCS based on IEEE 802.11 Wireless Local Area Network (WLAN), which provides flexibility, reduced infrastructure costs, and greater convenience. The IEEE 802.11 standard MAC protocol includes the DCF and the PCF. The DCF is designed for asynchronous data transmission, while the PCF is designed for real-time data. The performance of a WLAN with DCF will fall when the number of wireless station increase in a basic service set (BSS). An advanced modified PCF (APCF) is presented to poll data from the AP to stations and response data from stations to the AP in CFP. The analysis indicates that APCF can improve communication performance, and is very suitable for large TCS.