During the 20-22 November Boat Racing Festival monks will be required to stay in their pagodas and watch the event on TV, said 85-year-old Non Gneth.
"For a monk to walk freely with crowds of ordinary people during the water festival violates the rules of the Lord Buddha," the patriarch said.
"If the monks walk freely, they will see women wearing sexy clothes or see people kissing. This violates their discipline,"
He added some younger monks carried mobile phones equipped with cameras at last year's festival and took pictures of people dancing, drinking alcohol and kissing - all of which are not allowed, including the possession of phones.
Monks are supposed to adhere to a code of Buddhist precepts that include celibacy and not touching or being alone with women, not drinking alcohol and leading a contemplative lifestyle without material possessions.
A committee has been created to curb bad behaviour among monks and if any are seen mingling at the festival they will be reprimanded and sent for a re-education class, Non Gneth said.
Authorities estimate around two million people could descend on the capital, Phnom Penh, for the annual festival.