The District Court heard that Siu Cheung-lung, 33, forwarded nearly 1,200 messages in his channel, which included using materials at universities to make bombs as well as calling on people to open the emergency doors on MTR trains.
In mitigation, the defence lawyer said Siu did not have any accomplices and the offences were committed during a short period of time.
The lawyer also said there were only around 20,000 subscribers in the channel, fewer than in other public groups.
He added his client had reflected on his serious wrongdoings during his 20 months in custody.
Siu will be sentenced next week.