A method for detecting an initial phase and a phase sequence in a permanent-magnet synchronous motor control system comprising a motor to be detected and an encoder coaxially connected to a rotor of the motor, comprising the steps of: acquiring through the encoder the following displacement data of the rotor sequentially: first displacement data which register the rotor's position at a Q-axis after the rotor spins from an initial position to the Q-axis; second displacement data which register the rotor's position at a D-axis after the rotor spins from the Q-axis to the D-axis; third displacement data which register the rotor's position at a negative Q-axis after the rotor spins from the D-axis to the negative Q-axis; and fourth displacement data which register the rotor's position at the D-axis after the rotor spins from the negative Q-axis to the D-axis; obtaining the initial phase of the motor based on the second displacement data, the fourth displacement data and the encoder's CPR (counts per revolution); and determining phase sequence of the motor based on the first displacement data, the second displacement data and the encoder's CPR, including: calculating a first difference between the first displacement data and the second displacement data; comparing the first difference with a positive or negative value of half of the encoder's CPR; and determining the phase sequence of the motor based on an outcome of the comparing step. acquiring through the encoder the following displacement data of the rotor sequentially: first displacement data which register the rotor's position at a Q-axis after the rotor spins from an initial position to the Q-axis; second displacement data which register the rotor's position at a D-axis after the rotor spins from the Q-axis to the D-axis; third displacement data which register the rotor's position at a negative Q-axis after the rotor spins from the D-axis to the negative Q-axis; and fourth displacement data which register the rotor's position at the D-axis after the rotor spins from the negative Q-axis to the D-axis; first displacement data which register the rotor's position at a Q-axis after the rotor spins from an initial position to the Q-axis; second displacement data which register the rotor's position at a D-axis after the rotor spins from the Q-axis to the D-axis; third displacement data which register the rotor's position at a negative Q-axis after the rotor spins from the D-axis to the negative Q-axis; and fourth displacement data which register the rotor's position at the D-axis after the rotor spins from the negative Q-axis to the D-axis; obtaining the initial phase of the motor based on the second displacement data, the fourth displacement data and the encoder's CPR (counts per revolution); and determining phase sequence of the motor based on the first displacement data, the second displacement data and the encoder's CPR, including: calculating a first difference between the first displacement data and the second displacement data; comparing the first difference with a positive or negative value of half of the encoder's CPR; and determining the phase sequence of the motor based on an outcome of the comparing step. calculating a first difference between the first displacement data and the second displacement data; comparing the first difference with a positive or negative value of half of the encoder's CPR; and determining the phase sequence of the motor based on an outcome of the comparing step.