The standard is to take a cheap bus to a small city to go on hitchhiking. I took a bus to Dujiangyan. In 2010 you could still see a lot of the destruction of the 2008 earthquake. But the trucks take you with them for free, and they are more comfortable than any bus.
Going South ==Going south towards Leshan you will want to get on a bus heading for the airport, and get of by the Homeland Hotel about 4 km before the airport. From there you turn left (with your back to the hotel), and walk over the airport express road with the heavy traffic. Soon you can get on the G4301 (ringroad), where you walk for a few km before you can turn right onto the G5. Just after the tollgate there is a gas station with a lot of cars filling up their tanks for a looong ride south who all want you to come along! Great hitching spot, although it takes some time to get there.
You can check buses going to the airport here http://www.cdairport.com/front_en/jt4.jsp I took the metro to the south railway station (2-3 RMB), from there I took a city bus 300, walked a while from the train station to find it, and they got me off the right place.
Ask the driver if he's going on the Chengya Gaosu, that's the highway between CHENGdu and YA'an. "Ni wang chengya gaosu neibian ma?".
Chengdu is the gateway to
the Tibetan Sichuan. The hitchhiking situation changes completely. Any people take you with them and the cities are small, so you can walk out easy.
Chengdu direction east: [http://cymytrip2.over-blog.de/article-von-chengdu-nach-danba-59020210.html]