You are waiting for 5 transplants. Taking into account the time of connections and the change of stations, the journey takes about 24 hours

Venice - Milan - Ventimiglia - Nice - Toulouse - Narbonne - Barcelona.

You can reduce the number of transfers to 4x, taking into account another route on the way about 26 hours : Venice - Dijon - Montpellier - Perpignan - Port Bo - Barcelona

We recommend choosing an airplane as a means of transportation. It is very advantageous for the price - a ticket for a low fire, if you buy it in advance, costs from 20 EUR one way, on the way about 1 hour 50 minutes