To transmit several frames of asynchronous data immediately, combined with the requirements of performance testing of a distributed fire control system. This paper proposes a method of transmitting serial data immediately with accurate time control for PC104 platform. The basic principles of real-time clock and serial communication on PC104 are discussed, and a reasonable interrupt control scheme was designed. The design of communication software includes real-time clock interrupt installation and handling, serial port interrupt installation and handling, and generation of testing data. The method has been applied to a fire control system in which testing data of each node can be aligned strictly on time line, and the precision of performance analysis was improved.