make same space between button in linearlayout

You can use layout_weight. But like you said Buttons will be stretched, so instead of using weight on Buttons, use on spaces(Views).

    <Button
        android:id="@+id/btnFacebook"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:background="@drawable/btn_facebook" />

    <View
        android:layout_width="0dp"
        android:layout_height="50dp"
        android:layout_weight="1" />

    <Button
        android:id="@+id/btnYoutube"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:background="@drawable/btn_youtube" />

    <View
        android:layout_width="0dp"
        android:layout_height="50dp"
        android:layout_weight="1" />

    <Button
        android:id="@+id/btnTwitter"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:background="@drawable/btn_twitter" />

    <View
        android:layout_width="0dp"
        android:layout_height="50dp"
        android:layout_weight="1" />

    <Button
        android:id="@+id/btnPintrest"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:background="@drawable/btn_pintrest" />
</LinearLayout>

To make your intent clearer in your XML use a <Space> instead of a <View> as follows:

  <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/Blue"
        android:orientation="horizontal" >

       <Space
           android:layout_width="0dp"
           android:layout_height="1dp"
           android:layout_weight="1" >
       </Space>

       <Button
           android:id="@+id/btnFacebook"
           android:layout_width="50dp"
           android:layout_height="50dp"
           android:background="@drawable/btn_facebook" />

        <Space
            android:layout_width="0dp"
            android:layout_height="1dp"
            android:layout_weight="1" >
        </Space>

...and repeat with the rest of your buttons...

</LinearLayout>

give layout_weight to every Button 1, it will divide all space