I figure it out,if you change –pod-network-cidr when you reinitialize kubernetes via kubeadm init,you should delete some auto-created things,just follow the steps below before you execute kubeadm init again:
execute Kubeadm reset on master and nodes.
execute etcdctl rm --recursive registry reset data in etcd.
rm -rf /var/lib/cni on master and nodes
rm -rf /run/flannel on master and nodes
rm -rf /etc/cni on master and nodes
ifconfig cni0 down on master and nodes
brctl delbr cni0 on master and nodes