Small armature induction high-speed permanent magnetism brushless D.C. motor non - position transducer control system is composed of amplitude limiting multiplepath switching unit, program control amplifier comparator, electric isolation circuit, current transducer, filter circuit, small armature induction permanent magnetism brushless D.C. motor, triphase inversion bridge and digital controller etc part. When PWM has larger duty ratio, comparing no conduction phase terminal voltage with supply voltage reference value, outputting phase conversion signal, when PWM has less duty ratio, comparing no conduction phase terminal voltage with armature winding midpoint voltage, outputting phase conversion signal, when armature winding and inversion bridge is disconnected due to fault, said digital controller still capable of obtaining motor rotor positional information. The present invention effectively solves phase conversion controlled problem, raising driving parts reliability and precision.