I have overridden the titleSpacing in the constructor of AppBar. But no difference in the title space.
new AppBar( backgroundColor: Colors.amber, title: new Text("Flying Dutchman", style: new TextStyle( color: const Color(0xFF444444), fontSize: 30.0, fontWeight: FontWeight.w900, ), ), titleSpacing: 0.00, centerTitle: true, elevation: 0.0, ) 
I wish to reduce the top space of the app bar title.
titleSpacing is not about the actual appbar height and top padding. It's the spacing on the horizontal axis.
AppBar is a prestylized component that follows material rules.
If you don't like these rules, don't use AppBar to begin with. And go create your own component ! :)
Here's an implementation example :
class MyAppbar extends StatelessWidget implements PreferredSizeWidget { final String title; const MyAppbar({this.title}); @override Widget build(BuildContext context) { return new Container( color: Colors.amber, height: preferredSize.height, child: new Center( child: new Text(title), ), ); } @override Size get preferredSize => const Size.fromHeight(40.0); } 
MyAppBar. Is there any other way to reduce size or can I add TabBar without AppBar?
TabBar is just a widget like any others. It doesn't need to be used with Appbar. You can very well add a TabBar to my example.MyAppBar.
Just make transform as root of text view and provide x value in nagtive.
new AppBar( backgroundColor: Colors.amber, title:new Transform( transform: new Matrix4.translationValues(-20.0, 0.0, 0.0), child: new Text("Flying Dutchman", style: new TextStyle( color: const Color(0xFF444444), fontSize: 30.0, fontWeight: FontWeight.w900, ), ), ), titleSpacing: 0.00, centerTitle: true, elevation: 0.0, ) 