The wire transport system is mainly a unidirectional winding system in low speed wire electrical discharge machining (LS-WEDM)at present,and the wire tension has a larger fluctuation and cannot be accurately controlled so that the processability of machine tool becomes poor.To counter the problems above, the major changing factors of the wire tension were analyzed in detail;the intelligent PID controller was designed by simulated annealing algorithm and PID control; the wire tension was feedback signal which was measured by pressure sensor, and the wire tension was closedloop and precisely controlled by magnetic powder brake and the speed difference of double motors; the voltage signal of pressure sensor was collected by oscilloscope, and the control effects of the two systems were compared by voltage signal. The compared result show that: the deviation of wire tension can be control below 1N, and the control effectiveness of double motors is slightly better thanmagnetic powder brake.