I am taking AirChina from Changsha->PEK->JFK, New York, is 2hr and 5 mins layover time enough?

Generally speaking, the minimum transfer time for domestic to international transfer in T3 is about 2 hours. Thus your time is tight. You are advised to complete procedures as soon as possible.
BTW, the correct procedures are the following:
Flight Arrival & Transfer Procedures - Inspection & Quarantine - Exit and Entry Frontier Inspection - Security Check - Customs inspection - Waiting & Boarding
Hope helpful!