Herein, the pulse-duration-dependent clamping intensity in a femtosecond laser filament is systematically investigated. The clamping intensity in the laser filament is directly measured. Results show that the clamping intensity gradually decreases as the pulse duration stretches from 45 fs to 177 fs. The experimental results are in a good agreement with the simulation results obtained by solving the nonlinear Schr?dinger equation. The analysis of pulse-duration-dependent clamping intensity in the laser filament provides scientific basis and new ideas for fully understanding intensity related filament applications.