This paper developed the electrothermal driving mechanism and the driving characteristics of three types of SMA actuators by experiment-based analysis. The results are: the bandwidth of actuators depends on the driving current, pre-tensile length, cooling speed and load; the restoring velocity of biased actuators is proportional to the driving current; the bandwidth of difference actuators is constrained to the cooling speed of SMA springs, it's necessary to control the driving current; difference actuators are better in driving characteristics than biased actuators; the difference actuators have a great potential for wide application in intelligent mechanical structures.