Navicat use mysql database connection error appeared in 1251, the workaround.

Direct modification

Open cmd, input administrator "mysql -u root -p [-h locahost -P 3306]" (within the brackets is the default content) Enter root password is entered into the MySQL client, then:

mysql> alter user root@localhost identified by 'newpassword' password expire never; mysql> alter user root@localhost identified with mysql_native_password by 'newpassword'; mysql> flush privileges;　　　　# 刷新权限

Which, "newpassword" is the new root user password.
At this point, Navicat can be connected successfully, the problem is solved!