The team, who already have Spaniard Carmen Jorda signed up in a similar role, added that the 25-year-old would undergo a development programme while taking part in the GP3 and GT Asia series.
"I'll be able to learn how an F1 team operates during race weekends as an integral part of the team and these invaluable experiences are going to lay the foundations of my future development as an F1 driver," said Fong in a statement.
"I aim to become the first Chinese driver to compete in a Formula One Grand Prix which will assist to promote the sport in China and also in Hong Kong."
Fong tested for Sauber last year in Valencia and took part in first practice in Abu Dhabi.
Lotus already have Britain's GP2 champion Jolyon Palmer as official reserve to race drivers Pastor Maldonado and Romain Grosjean.
(Reporting by Alan Baldwin, editing by Sudipto Ganguly)
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