The victim a resident of Udapussellawa had been on duty with two other female soldiers at the second security post.
She had taken over the shift from midnight to 2.00 am while the rest had gone to sleep and had then shot herself in the chest with her T-56 weapon.
The victim was soon rushed to Trincomalee hospital but was found dead on admission.
China Bay Inspector Clement Fernando said the reason for the suicide was not known.
"Her past records have been normal and the only significant fact is that the victim had not taken her dinner on Tuesday night", the OIC said.
The body of the soldier is at the Trincomalee hospital morgue awaiting the post mortem examination.
