Autologous blood transfusion, i.e. "storing my own blood to be used by later time", is considered a kind of doping. Why is this practice banned like taking drugs when there is clearly no external substance used?
Because it is a way to enhance performance, in an unnatural way. It basically has a similar effect as EPO: increasing your red blood cells. It can be very dangerous if done incorrectly, which is probably one of the reasons to ban it as a form of discouragement.
One of the most dangerous things that can happen is when the blood is if not stored correctly you can get severe infections which can make you very ill, in extreme cases if could end up being lethal. You can look up Riccardo Ricco for example, an Italian pro cyclist who tried using blood doping in 2011 which caused sepsis and kidney failure.
Increasing your red blood cells in a natural way, for example training at altitude, is allowed.