See : https://www.seat61.com/trains-and-routes/madrid-to-lisbon-by-train.htm

It's a long journey but doable

A bus will be quicker... (Flixbus or other)

@thibcabe  would be the trains included in the interrail pass?

Yes but you need seat reservations for the Madrid - Badajoz leg (+ Entroncamento - Lisbon). The first one is available at any Spanish train station, the second one in Entroncamento when you arrive.

I think it's explained in the first link I posted

This link too can be useful :

https://www.seat61.com/international-trains/trains-from-Madrid.htm#Spain-Portugal

@thibcabe  but the trains are not on the list: https://www.interrail.eu/en/plan-your-trip/tips-and-tricks/trains-europe/railway-companies

The Spanish trains are run by RENFE, the Portugese by CP.

That mean, i can travel with all trains in the countries?

Yes obviously :)

The Interrail/Eurail pass covers at least 95% of European railways and all major mainlines

Although all national rail operators and quite a few private operators accept passes, there are a growing number of operators running new low-cost services not valid with a pass. Confusingly many of these are part or fully owned by the national carriers. Examples in Spain are Ouigo (also in France) owned by SNCF, Italo in Italy and Iryo in Spain.

In almost all circumstances there will be a parallel service on the routing operated by the national carrier.

Although not perfect the planner will usually indicate if a specific journey is not part of the network.