Fang Dongbing, 46, was sentenced to a year in prison and fined 10 million yen (USD 83,000) after being found guilty of illegally harvesting coral in waters near the Izu island chain, some 600 kilometres south of Tokyo, in December.
Prosecutors had sought 18 months in prison and a 15 million yen fine, after Japan revised its laws on illegal fishing, tripling the maximum fine for poaching to 30 million yen last year.
Japan's coastguard last year reported a surge in the number of Chinese boats fishing for coral in Japanese territorial waters.
Coral is popular in parts of Asia for use as ornaments and for jewellery.
Official vessels tend to chase the poachers away from the uncontested area, and the incidents rarely cause major friction between Tokyo and Beijing, although the two sides remain at loggerheads over ownership of an island chain in the East China Sea.