<Window x:Class="DataGrid_AutoSize.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="500" Width="800">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="376*" />
            <ColumnDefinition Width="402*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="65" />
            <RowDefinition Height="396*" />
        </Grid.RowDefinitions>
        <Border BorderBrush="Silver" BorderThickness="1" HorizontalAlignment="Stretch" Margin="5" Name="border1" VerticalAlignment="Top" CornerRadius="5" Height="50" Grid.ColumnSpan="2">
            <TextBlock Name="textBlock1" Text="DataGrid ScrollBar Demo" Margin="15,15,0,0" />
        </Border>
        <Grid  Grid.Row="1"  HorizontalAlignment="Stretch" Name="grid1" VerticalAlignment="Stretch">
            <DataGrid AutoGenerateColumns="False" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" x:Name="SrollBarDataGrid">
                <DataGrid.Columns>
                    <DataGridTextColumn Width="100" Binding="{Binding id}"/>
                    <DataGridTextColumn Width="100" Binding="{Binding text}"/>
                </DataGrid.Columns>
            </DataGrid>
        </Grid>
        <StackPanel Grid.Column="1" Grid.Row="1" HorizontalAlignment="Stretch" Name="stackPanel1" VerticalAlignment="Stretch">
            <DataGrid AutoGenerateColumns="False" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" x:Name="NoSrollBarDataGrid">
                <DataGrid.Columns>
                    <DataGridTextColumn Width="100" Binding="{Binding id}"/>
                    <DataGridTextColumn Width="100" Binding="{Binding text}"/>
                </DataGrid.Columns>
            </DataGrid>
        </StackPanel>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.ComponentModel;
using System.Collections.ObjectModel;
namespace DataGrid_AutoSize
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            Init();
        }
        private void Init()
        {

            ObservableCollection<Test> mytestdata = new ObservableCollection<Test>();
            for(int i=0;i<200;i++)
            {
                mytestdata.Add(new Test(){id=i.ToString(), text="name"+i.ToString()});
            }
            SrollBarDataGrid.ItemsSource = mytestdata;
            NoSrollBarDataGrid.ItemsSource = mytestdata;
        }
    }
    class Test 
    {
        public string id { get; set; }
        public string text { get; set; }
    }
}