Abstract. High Altitude GAmma Ray (HAGAR) telescope is an experiment for detection of very high energy gamma rays from astronomical sources. This telescope array located at an altitude of 4270 m at Hanle, is the highest altitude atmospheric Cherenkov telescope in the world. This experiment indirectly detects gamma ray primaries through detection of Cherenkov light from extensive air showers. Performance of this experiment can be understood only through Monte Carlo simulations of extensive air showers and modeling of HAGAR telescope response. Details of these simulations are presented along with the comparison with experimental data.