Abstract Using four MMS satellites from 2015 to 2021, we statistically investigate Electron Cyclotron Harmonic (ECH) wave power scale lengths. These waves are categorized into three distinct populations based on the background magnetic field topology: equatorial, off‐equator, and near the magnetopause. Generally, the observed scale lengths range from several kilometers to 100 km, with a typical value of ∼10 km. For the equatorial population, the typical parallel and perpendicular scale lengths are ∼14 and 24 km, respectively. For the off‐equator population, the parallel and perpendicular scale lengths are typically 20.8 and 19 km, respectively. For the population near the magnetopause, the parallel and perpendicular scale lengths are 19 and 13.7 km, respectively.