The suspects were caught in the country's Jiangsu Province after police received a tip off from a university employee.
Police also seized more than 140 guns, hundreds of rifle components and more than 40,000 bullets, state-run Xinhua news agency reported.
In September last year, police in Xuzhou City discovered three gun barrels in a parcel delivered from Taiwan to a university employee after a tip-off.
Police searched the suspect's house and found gun manufacturing tools, one imitation air gun, 225 gun barrels, more than 4,000 lead bullets and piles of rifle components in his basement, which resembled an armoury.
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After being questioned by the police the employee said he had become acquainted with a seller surnamed Xie from Taiwan via instant-message service in early 2013 and became a sales agent for the Chinese mainland.
He said he was a military fan and had allegedly purchased gun components from Xie before selling them to others through the Internet.
The employee had even bought steel tubing, which he gave to a local company to produce gun barrels so he could develop his own brand.
Further investigation is under way.
China bans the manufacture and sale of guns in order to control violent crime.
Private citizens are not allowed to own guns.
According to Chinese law, a person can be sentenced to prison for up to seven years if convicted of illegally owning a gun.