Abstract: For the measurement of sound attenuation of active noise reduction insert earphones, four typical measurement methods are comparatively studied, including real-ear attenuation at threshold (REAT), loudness balance (LB), microphone-in-real-ear (MIRE), and acoustic test fixture (ATF) methods. According to the characteristics of the earphones, the measurement devices, experimental environment, and experimental procedures are designed, and the measurement studies of three earphones are carried out. The results show that for passive sound attenuation measurements, the results of the MIRE method are close to those of the “gold” standard—REAT method in the middle and high frequency range, with a difference of ±3 dB, and more accurate at low frequencies. For active sound attenuation measurements, the results of the MIRE and LB methods are close to each other, with a difference of ±2 dB, and the MIRE method is easier to operate. The MIRE method has high test efficiency and accuracy and is an effective method to measure the sound attenuation of active noise reduction insert earphones.