SA led 3-0 at half-time and have to win the Japanese tournament if they are to participate at the London games in July.
Justin Reid-Ross opened the scoring midway through the first half with a goal from a penalty corner (PC), before Ian Hailey added the second five minutes later, from a breakaway involving Thornton McDade.
Lloyd Norris-Jones then scored the third, three minutes before the break after a strong deflection from Rhett Halkett.
Robinson opened the scoring in the second half to score SA's fourth, while China pulled a goal back straight away.
Robinson then added his second in the space of two minutes to restore SA's four goal margin.
Goalkeeper Rassie Pieterse showed his class by keeping the Chinese strikers at bay, making an excellent double-save 12 minutes before the end from a Chinese PC.
China eventually scored their second goal after continued pressure, which was converted from a PC awarded a minute from time.
The win sees SA remain in second place, level on points with Japan, who earlier on Monday beat minnows Brazil 11-0 in a dominant display.
SA have scored 22 goals from their first three matches of the qualifying tournament.
The top two sides after five matches will compete in the final on Sunday, where the winner will qualify for the Olympics.
SA's next fixture is against Japan on Wednesday.