Can i create a 1mx1m poster using keynote??

I will hazard a guess that (1mx1m) means 1meter?

Keynote is not a good application to print from, there is no control over scaling in Keynote so a 50cm object will print much smaller than 50cm.

Use a graphics or page layout application that can scale to print correctly; Photoshop, Indesign, Pages, there are many others.