My baby girl now 1year and two months but weighted only 8kg.she is not gaining the weight compare to her intake. she born as underweight of 1.7kg.

Good progress : if your baby was 1.7 kg at birth and 8 kg at 14 months, that is good progress. Her continued weight gain depends upon her overall health, any ongoing medical condition invluding the reason she was underweight at birth. If she was premature, without any significant medical issues, it has its own trajectory for catch up growth. Your baby doctor needs to examine the child for any further testing.

Low birth weight: Relax a bit. I have twin granddaughters whose combined birth weight - 8 weeks early - barely made 2 kg. They are now 9 years old and doing very well. That said, please see your pediatrician to confirm that your baby girl's weight is growing OK.