Haha, I found solution in a useful topic.
And now I know, vsearch just does the classic OTU clustering, which means, I need to Clustering and followed by chimera filtering and aggressive OTU filtering. Just like the picture shows:
But for a Dada2 results, use the table.qza and rep-seqs.qza to do taxonomy analysis and diversity analysis is recommended!
This forum is really useful! 