With a steadier hand in the final rounds, Jin prevailed over Vietnam's Xuan Vinh Hoang, a 41-year-old who made history on Saturday by winning his country's first-ever gold medal, in the 10 metre air pistol.
Kim Song Guk of North Korea, 30, won the bronze.
The crowd cheered the exciting comeback by the 36-year-old Jin, ranked No. 1 in the world. He is one of the Olympics' most decorated pistol shooters, having won the 50 metre titles at Beijing and London, where he also claimed the 10m air pistol event.
He now has six Olympic medals, including four golds, but called Wednesday's addition his "best gold medal."
Having qualified in first position out of eight, Jin got off to a wobbly start. A third of the way through the competition, he was nearly five points behind the leader Hoang, and at risk of being cut.
"I told myself don't give up, don't give up," Jin said. "I wanted to give up. I was doing badly, but I said to myself this is my last Olympics. I cannot give up."
With the cool head of a four-time Olympian, he gradually closed the gap as Hoang faltered, and surpassed him in the final rounds, ending with 193.7 points to Hoang's 191.3.
North Korea's Kim said he had hoped to do better than bronze, his country's third shooting medal.
"It is only gold (that matters)," he said. "I didn't do as well as expected. It is my first Olympics and I feel I am not up to standard yet."
