Haw many antivirus we can use it in our computer??

Basm Allah Alrahman Alrahim

million !

but don't use them at the same time , by stop them from services and start up look to this Question and answers

Thank you for this question that help us to search and learn

Only one 

The risk of installing two anti virus is like in the police force where you have let say FBI and Police working on a case , there is a risk someone assume the other to already done a check, then the file is completely ignored. You are also using more resources. FBI and Police are known to argue about jurisdiction conflicts, your Antivirus will too. They might try to reach same resources, conflicting each other out then crash.

If you would want to benefit from multiple company Antivirus databases, you could install multiple On Demand scanner . But install only1 Real Time/ On Access Scanner.

Stuff like Malwarebytes (free version, paid version has Real Time scans although they claim it wont cause conflict), Hitman Pro , Norton Security Scanner is some example of On Access. Most of the on access scanneris free. 

The antivirus program checks every file you open or download for malware.If you have more than one antivirus program running at the same time--or more than one firewall--you're asking for trouble. Two such programs, trying to do the same thing at the same time, will slow down your system. Worse, they can cause conflicts.