What is the name of the domain?
any-short.com
What is the issue you’re encountering
After using cloudflare my website got attacked by bot spammers, this week I got 10k+ bot traffic that never happened before using cloudflare. My website goes down several time in a week since i use cloudflare service. I don’t know whats wrong or cloudflare do this on purpose. Even after I stop using cloudflare my website still got spammed by bot
Was the site working with SSL prior to adding it to Cloudflare?
Yes
What is the current SSL/TLS setting?
Full (strict)
Do you see that in your origin server logs or in your cloudflare analytics or both?
That means the attackers know the IP address of your origin server and are able to attack it directly. You should ask your hosting provider to lock down the origin to only accept traffic from cloudflare IPs 
this site for details on how to do that.
Both on my server and cloudflare analytics
But how they know to attack my website in first time? My website online for 6 month without any problem but get spammed a day after I use cloudflare. Most of bot comes from country that never hit my website before, are there some bot specifically crawling a website in cloudflare service network?