is it possible or easy for a pakistan to travel to yunnan

try contacting the chinese embassy in pakistan. they'll tell you the visa requirements.

pk.chineseembassy.org/eng/lsfw/va/

Once you have a visa then comes the challenge of getting flights. I found that Emirates operates from Karachi, and probably other cities and will fly to Beijing (and probably other cities).

I also looked at one page Air China put up and for some reason all of the flights from Pakistan originate in cities in India.