For situations with large load and low speed operation, the traditional sensorless control technology of microBrushless Direct Current Motor (BLDCM) has the problems of starting reversal and difficult starting. First, the relationship between phase inductance and rotor position is analyzed based on Ampere circuital theorem. A method was designed to determine the rotor position by injecting a certain sequence of voltage vectors according to its current response. The control system model was built by using Matlab/Simulink. The experimental results show that microBLDCM can start from any position without inversion under heavy load and can running at low speed.