The accused CRPF personnel named Ajit Kumar is critical in a hospital.
The three personnel who were fired at by their colleague, died at the 187th battalion camp of the force in the Battal Ballian area in Udhampur. The personnel first got into an altercation after which the shooting took place.
The alleged fratricide incident happened at around 10 pm when constable Ajit Kumar shot three of his colleagues from his service rifle.
Kumar hails from Kanpur in Uttar Pradesh and was rushed to a military hospital nearby, they said.
The deceased have been identified as head constables Pokarmal R of Jhunjhunu in Rajasthan, Yogendra Sharma of Delhi and Umed Singh of Rewari in Haryana.
The incident is said to be triggered after the jawans had an altercation, they said.
Senior CRPF and police officials have rushed to the spot.