Avast doesn't usually falsely flag NHSEO but it has been known to. Sadly there is nothing I can do to improve their flagging algorithm so you will just have to set an exception for it or disable it while NHSEO is running.
I think Avast is one of the annoying AVs that, while No Hands SEO is posting, will constantly pop messages up stating that a potentially harmful page is trying to be loaded but there is no part of NHSEO that will run any type of code so malicious code will never be run and these messages are pointless as far as NHSEO goes.
I guarantee that there has never been a single user ever get any sort of virus, malware, Trojan or any other type of unwanted software installed to their system by using NHSEO. My preferred Av software is Microsoft Security Essentials (installed by default as defender in Windows 8 and 8.1) as it never seems to needlessly false flag software and does a very good job of protecting a system without being at all intrusive, it is totally free and in my experience far more reliable than others.
>>>so you will just have to set an exception for it or disable it while NHSEO is running seems this is not a good experience as I m facing now. Though i can restore NHSEO.exe from Avast Virus Chest, it will recactch this EXE again and again after I turn on my antivirus. It keep complaining NHSEO.exe is infected with EVO-GEN. Or even I disable antivirus, once I turn it on, it will move NHSEO.exe to chest again.
You need to set an exception for it and/or the folder it is installed to. Just reinstating it whenever it is removed likely won't have much of a difference as it won't prevent it from being falsely flagged in the future.