Is it compulsory to pray 3 rakah of vitr after Isha .If some one not pray then it’s Isha prayer will accepted or not ?
Witr is not mandatory.
Your isha is not effected by this.
It is a highly recommended Sunnah. The Prophet salla Allahu Alaihi wa sallam used to never miss witr and the 2 rakahs Sunnah of fajr even while he was traveling, but this is not mandatory.