what was the major economic contribution of the Sui dynasty?

Equal-field system was still applied. Meanwhile, taxation system of payment in kind and labor was adopted too. They promoted the agricultural development. During the Tang Dynasty, these two measures were still used. Most importantly, Grand Canal was built. It's true that many people were forced to work for the canal. However, this canal strengthened the communications between northern and southern regions. Thanks to this canal, goods could be transported between north and south.

Some historians comment that Sui's Economy was the fundament for the Tang's Prosperity.