Ultra-fine powder extinguishing agent (UPEA) concentration measurement is essential for evaluating the validity of aircraft nacelle fire extinguishing system. Based on Beer-Lambert law, the influence of powder contamination, ambient light, and other factors on the measurement signal during high-concentration measurement by the extinction method has been analyzed. We proposed a correction model of the relationship between transmittance and high mass concentration of powder. An optical fiber UPEA concentration measurement device based on the extinction method has been developed. Meanwhile the calibration test platform for the occurrence of stable and uniform concentration powder has been built. The mass concentration of sodium bicarbonate UPEA that is promising halon replacement agent in aircraft nacelle is analyzed by developed device. The results show the modified relational model function fits the test data well, and the device measures concentrations up to 128.8  g  /  m³ with an indication error of 11.7%. The present work provides a new concentration measurement method for high-concentration powder measurement, especially the real-time measurement of UPEA concentration.