A simulation study for Cherenkov light images of extensive air showers
was performed to develop a method to distinguish the nuclide of
ultra-high energy cosmicrays. Cherenkov telescope of 3m diameter
was assumed to be installed in the Tibet highland of 4300m.
As a result of the simulation, Vertical length (LENGTH) ,
fatness (FATNESS) and the rising altitude of air showers (X20)
of Cherenkov images were examined variously. Showers
with LENGTH of 2.0$B!k(B or more are found to be originated by
protons, and showers with FATNESS greater than 0.9$B!k(B
are known to be originated from very heavy nucleus as iron.
It was found that air showers with X20 less than 0.9$B!k(B
are originated form Fe nuclei, and for showers with X20
greater than 1.5$B!k(B the primary cosmic rays are limited to proton.
Incident energies of air showers are estimated with an error of
20% for protons and 14% for irons.