在最外层使用

RelativeLayout作为根节点，同时设置

android:fitsSystemWindows="true"
问题解决．

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/white"
    android:fitsSystemWindows="true">

    <android.support.design.widget.CoordinatorLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <!--标题栏 Toolbar-->
    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">
        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:minHeight="48dp"
            android:layout_height="48dp"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme" />
    </android.support.design.widget.AppBarLayout>