Abstract: The design of threshold temperature actuator is the key technology for the quasi-distributed fiber optical temperature annunciator system to locate the position where the temperature alarm is taking place. Therefor the principle of designing the actuator based on OTDR （optical time domain reflectometer） and SMA （shape memory alloy） are analyzed, and the actuator＇s physical model are put forward too. By experiment research such SMA spring that meet the actuator＇ technical specififcations had been chosen from the samples. And then the actuator＇s mechanic design are implemented by making use of that SMA spring. The system＇s running show that the threshold temperature actuator can operate efficiently and that the system can realize quasi-distributed temperature alarm, and moreover the system has such excellent performance parameter as spatial resolution approaching 1.5 meter and response time under 16 second.

Key words: threshold temperature actuator, shape memory alloy（SMA）, OTDR, force of restitution, test