The first suspicion that China would launch a manned spacecraft into space raised in when China recovered a satellite from orbit in 1975.
Manned spacecraft is really a natural next step after that.
Such an achievement also has great political and military value that China urgently need at that time like Soviet in 50s and 60s. In 1979, A Shanghai newspaper, Wen Hui Bao, published a photo shown a Chinese astronaut in training in space suit and a helmet. Soon later, another Shanghai based magazine, Science Pictorial, released more detailed astronaut training photos. These color photos shown the simulated space cabin, space suit, and even space food clearly. The magazine also revealed the largest centrifuge in Asia used in astronaut traning.