Is it possible for english teacher to use english without mix mother tongue everytime he/ she teach?

Yes,it is 

In my opinion, 
      one still may be use the mother tongue as may be in teaching and learning materials that will be easy to say will understand and be understood by students if the explain  little use mother tongue.
We know the mother tongue is the language that first time we know the language and the first time we can speak.
To clarify and simplify the process of learning and teaching, a teacher uses language that is easy to understand and be understood by students.
And we know that language is a key element in teaching and learning.
and mother tongue is the first language for someone who is new to the language.
and possible a teacher make use mother tongue in english learning.

English teacher and native speaker

Between english teacher and native speaker is enough different.

         If I think English teacher with Native speaker has advantages and disadvantages of teaching process in my opinion.in english teacher is clear and it's delivery more attractive, easily understood and easier vocabullary.
 to a listener may pronuncation delivered less good, but easy understood by the listener.
And the methods used also different from the native speaker. native speaker may ues methodes that give more priority to proununcation.
        English teacher more clearly understood when to submit the material in the structure or grammar.
If for speaking or pronuncation language better teacher. Because of their everyday english , and than a native speaker will be very fluent in pronuncatiion and more clearly.