Chinese submariners are different. In the United States, submarines have crews that stay with the boat, just like on any other warship. The only exception is the SSBNs (ballistic missile subs), which have two crews, so that the boat can spend the maximum amount of time at sea. The Chinese do it differently. Each class of subs has crews trained for different types of missions, and these crews are assigned to a sub in order to train in their specialty (mine warfare, anti-surface warfare, and anti-submarine warfare). Another reason for the multiple crews (usually two per sub) is also to increase the number of trained crews ahead of the introduction of many more new subs in the next decade. The Chinese have recognized, and accepted the fact, that it takes over a decade to train effective submariners, particularly the Chief Petty Officers (the Chiefs) who really make a boat work. The chiefs were given a big pay raise five years ago, and made to understand that being a naval NCO was a good, and lucrative, career choice. 

The only flaw in this plan is the poor condition and reliability of Chinese submarines. Chinese boats are either bad copies of Russian designs, or even worse attempts to build Chinese designs. But the Chinese know that just having submarine crews is not enough, you have to get these guys to sea, as much as possible. Under the old Soviet system, the sub crews spent most of their time living in barracks, and getting lectured in classrooms, or doing dry runs while their sub was dockside, motionless. When Soviet subs did go to sea, it was for a day, and then back to port and the barracks. By the end of the Cold War, the Russians and the Chinese were convinced that the Western approach (keep the boats at sea as much as possible) was ancient wisdom that still applied, and worked. 

The Chinese submariners have to work for their higher pay. Keeping their creaky boats at sea means a lot more maintenance and repair work in port, and a lot more alertness and tension at sea. There are more accidents as these boats are pushed beyond what they were designed for. The Soviet design theory held that you built subs that spent most of their time in port, and then went to war and maybe survived a few weeks or months, and maybe got a shot in. This didnt work for the Soviets during World War II, but they stuck with the concept during most of the Cold War. Now China is trying to design and build a new generation of subs on the Western model (spend lots of time at sea in peace time, and be good enough to kick ass and survive in wartime.)