what transportation can we use to reach chongqing from Leshan?

Well, I heard that only Xiaoba Tourist Bus Station has one long-distance bus scheduled at 10:40. The duration is 5 to 6 hours. It costs CNY 123 per person.
So taking train is a more efficient way for you.
Take train from LS Railway Station, get off at Chengdu East Railway Station.
It takes around 70 mins. First class seat is CNY65 and second class seat is CNY54. Then transfer to bullet train to Chongqing North Railway Station. The travel time is around 2 hours. First class seat is CNY116 and second class seat is CNY96.5.