After taking the lead halfway through, Huang powered home in a time of 4:52.36.
British rower Aggar, who has not been beaten since the Beijing Paralympics, finished in fourth place and said that he was disappointed with the result.
"I'm devastated. I was obviously the favourite going in and I wanted to win," Aggar told Channel 4.
"I went out hard but my race fell apart in the middle. I tried to dig deep towards the end but I had nothing there.
"It just wasn't my day today."
Aggar had been one of the favourites for a British gold medal.