in general, you need an NOC, CEID Clearance, Letter to MoL from your existing employer.

details are below

plz follow the link:

http://www.gov.qa/wps/wcm/connect/cnt/en/1_home/11_citizens_and_resident...

Transferring Sponsorship

Description of Service
This service is for residents who wish to transfer their visa sponsorship to a new sponsor institution covered by Ministerial Resolution 11 for 1997.

Target Audience
Residents
Those wishing to work in institutions covered by Ministerial Resolution 11 for 1997.

What you need to do
Submit the required documentation to the Department.

Required Documents
Application addressed to the Department of Labour along with the registration from the company.
Copy of academic qualifications.
Copy of a valid passport.
Non-objection letter from the current sponsor.
Certificate of good conduct issued by the Ministry of Interior.