Googlebot crawl request of my site has dropped nearly over 95%

Googlebot crawl request of my site has dropped nearly over 95% at 12:00am on 9th, Oct (GMT+8) .We have no idea what’s going on.

We want to know whether there is an update of google about crawlling, or is this the issue of our own site? If something is wrong with our site, in what aspects would you recommend us to check, analyze and accordingly optimize? Looking forward to your reply.