You have not explained why the need arises for your query. Isn't it that your present employer refused to give a certificate of experience? Normally, an Experience Certificate is issued when one leaves any organization. In your case, you are still employed, and you wish to attend an interview, requiring a certificate of employment from your present employer to show them, am I correct?
First, ask them for such a certificate, and if refused, you can show your appointment letter and other documents like a bank passbook, etc. Acceptance of these circumstantial evidences depends on the requirements of your prospective employer. You cannot take them for granted. For instance, when your competitors produce valid certificates, you, without such a certificate, how can you be preferred? But still, exceptional candidates can be selected, and appointments could be reserved subject to the production of necessary credentials.
Don't panic; try to obtain it and give it a try. All the best.