There were several technological advances in the Early Middle Ages that paved the way for the High Middle Ages.
One was the invention of the horse collar. Another was the heavy plow. Another was the three field system of crop rotation. Yet another was the horse shoe. Among them these increased agricultural production in Europe quite a lot, making it possible to support the towns and cities of the High Middle Ages.
Another set of technologies were the invention of the stirrup and the arched saddle. These combined with the introduction of a new type of lance and the tactics to use it radically altered the technology of warfare and made the mounted knight paramount on battlefields of the High Middle Ages.
There is an important point to be made here, however. The advances that caused Europe to pass from the Early Middle Ages to the High Middle Ages were more social and political than technological. The technological developments above were not things developed or invented immediately before the High Middle Ages, but introduced over a long period, and their effects accumulated slowly.