In order to test the ability of phase diversity in piston detection of segmented telescope,a simulated segmented experiment was performed by masking two apertures (200 mm and 50 mm)on a spherical reflective mirror.The biggest error of piston in the experiment is less than 25 nm for the 200 mm experiment and 1 nm for the 50 mm experiment after calculation.Through the experiment,it is proved that the phase diversity is feasible in piston detection of segmented telescope.That lays the foundation to detect piston in practical segmented telescope.