Train from Rome to Veince

If you are going to Venice proper, the train station in Venezia Santa Lucia (Venezia S Lucia). This is the terminus so you don't have to worry about missing the station. Roma Termini to Venezia S Lucia is about 3hrs 40 minutes on the fast trains. trenitalia.com has an English version. You will find different prices - Super economy, economy and base. The base is the normal price you would pay if you walked into the station and bought the ticket just before you get on the train. The others are cheaper and you would have to buy them ahead of time but you are locked into the time and cannot change the reservation or very limited change may be allowed. If you know exact times of when you want to travel, you can purchase the super economy or economy tickets. Look at roninrome.com for details.
http://www.roninrome.com/transportation/trenitalia-changes-fare-structure#more-18639 I bought Venice to Florence tickets at the super economy rate (formerly called mini fares) ahead of time because I was sure of the time of travel but bought the Florence to Rome a couple of hours before travel paying the base price. Just curious - you say that you are going to Venice and back to Rome. Is it because you are flying in and out of Rome? Have you considered flying into Venice and flying out of Rome or the other way around? We flew into Venice and out of Rome and the fare was not much more expensive. Rome had more flights than Venice.

There are only two train stations in Venice. The one you want, as stated by Nalayini above, is Venezia Santal Lucia. The other station is Venezia Mestre. This is the stop before Santa Lucia. If your travel is within 120 days out, you can buy your tickets now. The advantage of buying now is that you can take advantage of fares as low as 9Euro each way. Ordinary fare is 76Euro. This is quite a deal if you are willing to accept non-refundable and non-exchangable tickets. This means that you have to plan well and be sure of your travel dates and times for this journey. If you wait until you get to Italy to buy your tickets, these nice economy fares will normally be gone and you will pay the 76Euro fare.

And at those low rates, you could even buy a couple of tickets in case you're concerned about missing the first train. It would still be an incredible bargain.

There are only two train stations in Venice Actually there are only 2 main ones. There are 4 in total. I took a Regionale from Mestre one year and got off at Porto Marghera by mistake, complete with all my luggage - good fun humping it right back up the stairs...

Don't forget to check Italo, the new competitor of Trenitalia!

We did this same trip a couple of years ago. Flew into Rome and out of Venice. I bought my train tickets prior to leaving home. I booked airfare and train tickets through a travel agent. I know you can buy tickets at the station but at the time I felt if I bought them at home it was one less thing for me to have to do there.