The host os is connected into network by wireless one so how to let its guest os connect network.
Take  as a reference. I run it successfully with following steps.
1, create /etc/qemu-ifup script and chmod it.
2, start a qemu guest os with command
sudo ./qemu/qemu-system-x86_64 -enable-kvm -m 1024 -drive file=marss_dram.qcow2 -vnc 127.0.0.1:0 -net tap -net nic