The capital of South Tyrol - Bolzano - is situated at one of the main European railway routes. So it can be reached easily from Munich and Innsbruck in the north as well as from Verona, Roma, Venice and Milano in the south.
From Bolzano you can reach the most important valleys and villages by train, all other places by public bus. More information to the public local traffic in South Tyrol you find here.
Furthermore there operates the Südtirol Transfer bus service.
Below you find an overview of the railway connections in South Tyrol.
From Munich Eurocity-trains start every two hours during the day directly to South Tyrol (via Innsbruck - Brennero - Bressanone - Bolzano). More Information and time tables on bahn.de and ÖBB Italia.
From Vienna via Villach to Lienz in East Tyrol, by regional trains further to the Val Pusteria and South Tyrol. More information you find on oebb.at.
From Switzerland by the Rhaetian Railway to Zernez , from there by bus crossing the Ofenpass to Malles in South Tyrol. From there by train (Ferrovia della Val Venosta) to Bolzano. More information on sbb.ch.