This project propose the influence of two non-ideal factors on zero crossing point (ZCP) detection based sensorless control of high speed brushless DC (BLDC) motor, i.e. asymmetric machine parameters and the resistance tolerance of back EMF measurement circuit. Influenced by the machine parameter asymmetry, the back EMF envelopes will shift horizontally from its ideal position. Further, the acquisition accuracy of back EMF is limited by the resistance tolerance of measurement circuit. Inaccurate acquisition of back EMF will result in vertical deviation of the envelopes. These two non-ideal factors decrease the commutation accuracy and deteriorate the control performance. In order to suppress the commutation errors, an adaptive threshold correction strategy, including horizontal and vertical corrections, is proposed for eliminating the influence of these two non-ideal factors, respectively. In addition, the proposed correction method does not depend on any parameters of the machine or the measurement circuit. Finally, the theoretical analysis and the proposed correction method are verified by experiment on a 54000-rpm high speed brushless DC drive platform.