Go to marriland.com or try Google marriland. They have the best Pokemon website ever created, they have walk throughs, all the pokedexs, If you need info then go to them, Also on U-tube there is a walkthrough of the entire game from marriland so just find the right video and you have it! (that was the only way I could get through victory road =] )
--IMPROVED ANSWER--
(From user "Fense")
1. Stock up on around 10 'Max Repels', 1 'Escape Rope' and 5 'Full Restores'.
2. Level up your Pokemon Until level 50-60, or have 1 Level 100.
3. Have 2 Bibearels (Sorry, I've forgotten how it is spelt), And teach them Hm's.
4. Teach your best Pokemon Tm's that are better than their original moves, if not or when finished, use PP- (Ups or Max's) on their best / most used move.
5. When done, Go to the Pokemon centre, and revive your Pokemon, and set journey towards Victory Road.
6. With all Victory Roads on all the games, its hard, so don't dawdle around.
7. Don't Bother to grab any items, Unless you manage to come across one.
8. Remember that you don't need Hm Cut going through Victory Road, I forgot to mention earlier.
9. Don't Jump down too many slopes, one could lead back to where you started.
10. If you Ever feel, Enough is enough, use your escape rope (this could also be the depletion of items stock).
11. If you used the Escape Rope, Do steps 1 & 5 again, But just those.
12. Then try again (I forgot to pin point when you got to Victory road).
13. And of course to the people who need directions use the Max Repels every time it runs out. And use Full Restores when your Pokemon are running out of HP.
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The best way to get past victory road in Pokemon Diamond is to buy lots of max repels and have a Pokemon that know the moves rock smash and strength.
you need the national dex
beat the Pokemon luegue then go to the Pokemon centre
You need to get all 8 gym badges and you need a Pokemon that knows surf and maybe cut in your party. Victory road is to the left of viridian town.
you beat the pokemon league and if youre talking about the one on victory road you have to get the national pokedex