Is it correct to add more deoxidizer to molten steel, and the less oxygen in the steel must be? why?

Incorrect, because the deoxidation element is added to the steel, on the one hand, it can deoxidize with oxygen to reduce the oxygen concentration, on the other hand, it affects the activity coefficient of oxygen. 

When the concentration of the deoxidizing element is high, since it lowers the activity coefficient of oxygen, the deoxidation reaction is hindered, and as a result, the oxygen content in the steel is increased.