Could you please tell me that what happen with my CV?Why employer does not chose my CV?

Usually, there are more people who want jobs that there are jobs.  Employers can therefore choose who to interview.  In the modern world, many employers and recruitment agencies do not respond to applicants who have not been shortlisted for interview: this saves them time and money, and avoids potentially awkward or embarrassing conversations.

With large companies and recruitment agencies, CVs are often reviewed by computers.  Only if the CV satisfies certain requirements is it forwarded on to a human.  These requirements are frequently based on keywords.  In other words, if your CV doesn't have the keywords the employer is looking for, your CV will never be read by a human.  There is no way of discovering what the keywords are, so you have to guess.

A substantial minority of jobs advertised do not really exist.  Employers may advertise a job for many reasons: internal politics, by mistake, to test the market, to scare current employees, to satisfy regulations, etc.  Sometimes the job has been filled before the advert is posted. 

Usually the employer has some kind of prejudice, conscious or unconscious.  (We all have unconscious prejudices, good people try to observe and overcome them.)  This can affect who gets invited for interview.

To get an interview, the following requirements must be satisfied.

1) The job really exists

2) The job doesn't get abolished before the interview date (for example, cost cutting or the hiring manager leaves.)

3) The CV has to have the correct keywords.

4) The computer has to be working correctly

5) The recruiter has to bother to check their incoming CVs that day, instead of just deleting the lot because they are busy

6) You have to not share the same name as the person who bullied the recruiter / employer in Primary School

7) The recruiter has to not fall out with the person in HR, and the person in HR has to not fall out with the hiring manager

8) Along the whole process, everybody has to not lose your CV

9) ....... well ok I think I've made my point. 

Employer use to filter the CV's according to job description so make your cv relevant that it look like best fit for the required post.