My dad had stroke since 1995. He is now double hemiplegia. Why is his pulse is around 60 averagely? Is it dangerous? He only lies on his bed everyday

Meds. I suspect it is due to his medications, but could be due to his neurological damage. In a healthy person that is a good pulse rate.
60 is not so bad. Considering the fact that your dad has double hemiplegia, he is therefore severely disabled and incapable of significant aerobic exercises which could increase pulse rate and enhance cardiac fitness. The one worry, assuming heart rate is regular, is insufficient blood flow to the brain if he were to rapidly go from recumbent or sitting to upright.