[..] What is this?
"Pretty self-explanatory" , I'd say. What part of it don't you understand?
I am working on this file for printer.
I asked whether i proceed with the warning and create the PDF.
Or this warning will have a impact on printer file.
I am not good at English
There are two things going on that the message is telling you. Your doument has a transparency blend space of RGB, which would be correct if the images are RGB, but would be incorrect if they have already been converted to CMYK.
Your export settings are specifying a conversion to CMYK, which might also be correct for press output where the printer cannot do the color conversion in the RIP. The message also implies that you are flattening transparency, which also may not be necessary, depending on your printer's requirements.
IN any case, this is a warning that there may be undesirable color shifts. You should go ahead and make a PDF, then look at it. If you find it is not what you want, try changing the transparency blend space inthe document to CMYK and try again.