I want to set-up zabbix on OpenWrt Router that can provide me to monitor the traffic of each connected client, and send an email notification to me when the traffic is abnormal.
opkg update; opkg find *zabbix*
I have already install all of zabbix packages
Lots of zabbix-related threads on the site.
Site search results -
More posts by same OP:
You were already told
opkg update
opkg install zabbix-agentd
Perhaps you should tell everyone you're trying to install the server and not the agent that monitors the OpenWrt device as you describe. Your device would have to have flash space and memory to install/run zabbix-server-frontend.
See: https://openwrt.org/packages/pkgdata/zabbix-server-frontend
Please be advised, installing this on the router itself is probably quite uncommon due to space requirements - if it will even work on your device. Usually this step is not OpenWrt-related, as it would run on a server. This is why you're not getting a lot of answers. 
(I almost think when the OP isn't satisfied, they just ignore the tread and make another. The OP seems to have wanted to install Server-end of Zabbix on OpenWrt since their first post mentioning the software - barely noting the agent that will run on OpenWrt.)