Milano to Venice
Since there are many cheap flights to Milan, many tourists go to Milano and then to Venice by train. Also you have the opportunity to spend one or two days at Milano and see the attractions.
Milan is close to Venice, only 280 km (170 miles) and the journey by train is under 3 hours. Check the train schedules at the official italian trains website.
There are two Milan airports, Linate International Airport (LIN) and Malpensa Intercontinental Airport (MXP).
Going to Venice from Milan Linate Airport
Linate airport is very close to the city, only 7 km (4 miles). There are frequent buses from the airport to Central Station for the train or Piazza San Babila metro station and the journey takes less than 30 minutes (depending on the time of the day).
From Central Station you can take a train to Venice Santa Lucia train station.
Going to Venice from Milan Malpensa Airport
Malpensa airport is 45 km (28 miles) northwest of Milan and has two terminals well connected by a free shuttle bus. From the airport you can reach Central Station or Porta Garibaldi Station. The trains for Venice leave from Central Station.
There are frequent buses to Central Station (every hour) and the journey takes less than an hour, depending of the traffic (that can be HEAVY so be careful with your timetable).
Also you can take Malpensa Express train that connects Malpensa International Airport to the centre of Milan (Cadorna Station). Keep in mind that you must go to Central Station to get the train to Venice.