<Grid x:Name="LayoutRoot">
<Button x:Name="BtnNavigateTabIndex" Content="NavigateTabIndex" Margin="152,200,0,190" HorizontalAlignment="Left" Width="120"/>
<TextBox x:Name="TextBox_1" HorizontalAlignment="Left" Height="48" Margin="120,64,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="80"/>
<TextBox x:Name="TextBox_2" HorizontalAlignment="Left" Height="48" Margin="120,128,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="80"/>
<PasswordBox x:Name="PasswordBox_1" HorizontalAlignment="Left" Height="48" Margin="224,64,0,0" VerticalAlignment="Top" Width="72"/>
<PasswordBox x:Name="PasswordBox_2" HorizontalAlignment="Left" Height="48" Margin="224,128,0,0" VerticalAlignment="Top" Width="72"/>
</Grid>
The design will will be like below.

If i click the button(NavigateTabIndex),The cursor should be navigate to TextBox or PasswordBox.
For EX: If you click the Tab Key in you Keyboard,the cursor would navigate.This is the scenario what i need .
In general there are a lot of gotchas with WPF focussing….some bugs even.
You need to understand the difference between Logical and Keyboard focus.
When using FocusScopes you can use:
MoveFocuswith aTraversalRequest(FocusNavigationDirection.Next)to change the logical focus to the next item in the scope.
An alternative to using FocusScopes is to track the GotFocus/LostFocus events and manage it yourself.
Some more links:
How to programmatically navigate WPF UI element tab stops?
Move focus in response to keyboard events in XAML
WPF FocusNavigationDirection, MoveFocus and Arrow keys
Locating the first WPF tab stop
http://www.codeproject.com/Articles/38507/Using-the-WPF-FocusScope
Ok here’s some example code for you. I took the liberty to redesign your use of the Grid a bit, to follow more conventional layout practice.