en the tone is different but the pronunciation is same

Hi, welcome to China. For people who are not the locals in sichuan province, including people from other parts of China, there might be a lot of trouble understanding them. But don't worry about it. If you talk to them in standard Mandarin, they will talk to you in Standard Mandarin, too. If you are lucky enough, you may meet people who can communicate with you in English. Good luck!

As some above friends said, there is diference between Mandarin and Sichuannise. In fact, Sichuanise is the one that close to Mandarin during many different dialect to some extend. I'm not sure how long you have studied Mandarin. Almost all the Sichuannese can understand Mandarin, but maybe some Sichuannese can't pronounce it standard. I think maybe you will have some trouble understanding people here, but less than you supposed. One way is that, turn to the young people, coz it's much possible for they can speak Mandarin and English. Anyway, good luck! You're so smart to choose Chengdu as your aim. Welcome to Chengdu, which is the city that you never want to leave after your coming.

they are not just a bit different. i would say, they are totally different , because people frome beijing cann't understand Sichuanise at all. my suggestion is: learn Sichuanise in life and forget Mandarin. I heard a lot that someone learn mandarin in Sichuan or Hunan, after four years they even don't know the difference between z,c,s and zh,ch,sh. that's horrible if you travel to north china with that mandarin someday. well, anyway, like England English and American English, if you don't mind that, just begin your way of Chinese learning.

there are some local slang and pronunciation sounds a bit different and they don't distinguish z c s and zh ch sh, in fact, only mandarin(beijing) features that.