The top seed never looked remotely troubled as he brushed aside his Austrian opponent, conceding just a single game in the first set.
The second set was almost as one-sided as Melzer struggled to make any impact, and the Serb took it for the loss of two games.
Djokovic will next take on Florian Mayer of Germany in the last four on the hard courts of Beijing.
Mayer beat China’s Zhang Ze in straight sets, 6-3 6-4, to secure his place in the last four.
Third seed Jo-Wilfried Tsonga beat Mikhail Youzhny of Russia 6-3 6-2 with consummate ease as he booked a spot in the semi-finals on the other side of the draw.
The Frenchman looked in sparkling form as he disposed of Youzhny, and will next take on Feliciano Lopez, who recovered from a set down to overcome Sam Querrey of the USA 4-6 6-4 6-4.
- Florian Mayer