The Spaniard, returning from a wrist injury, beat qualifier Peter Gojowczyk 6-3 6-4 in an hour and 45 minutes to set up a last eight clash with Martin Klizan at the ATP 500 event.
"In general I need to improve," said Nadal who won 85 per cent of his first service points against his German opponent.
"It's obvious. My serve worked well today. But in general I need more rhythm on the legs, more rhythm on the shots.
"I am playing okay, trying to not miss a lot, trying to play with not too many risks. That's what I did today. It's the only way to have matches, only way to have rhythm," he said.
"Coming back in this part of the season is completely different than if I am coming back on clay. I would be able to be in rhythm a little bit faster, a little bit easier...
"For me this last part of the season obviously is important. Every tournament is important for me. At the same time I want to finish with a better feeling possible to start the new season with good tennis," he added.
Slovak Klizan was leading 6-2 3-0 when seventh seed Ernests Gulbis retired due to a shoulder injury.
Third seed Tomas Berdych moved up a place to seventh in the race to the season-ending ATP World Tour Finals in London after his 6-3 6-4 victory against wildcard Viktor Troicki despite a poor serving display.
The Czech only managed to make 32 percent of his first serves and now meets eighth seed and big server John Isner in the quarter-finals.
Elsewhere on Beijing's blue hard courts, Bulgarian Grigor Dimitrov beat Spaniard Pablo Andujar 6-4 6-4 to set up a quarter-final clash with world number one Novak Djokovic, while sixth seed Andy Murray overcame Pablo Cuevas 6-2 6-2.
In the women's section, Russian Svetlana Kuznetsova upset seventh seed Angelique Kerber in three sets, while Petra Kvitova also reached the quarter-finals without hitting a ball after American Venus Williams withdrew with a viral illness.
Twice champion Kuznetsova dropped the first set but eventually prevailed 2-6 6-4 6-3 in the two-hour-and-eight minute battle that complicates her German opponent's hopes of qualifying for the season-ending WTA Finals in Singapore.
Kerber is ninth in the race for next month's event featuring the top eight players and could have improved her position with a better showing in China.
Second seed Simona Halep, one of the four players to have already secured a place in the Singapore event, battled past Andrea Petkovic of Germany before withdrawing from the tournament having aggravated a hip injury in the process.
The Romanian, who produced 91 errors, fought for more than two and half hours to tame Petkovic 7-6(4) 5-7 7-6(1) before giving a walkover to Ana Ivanovic, who downed Sabine Lisicki 6-3 7-5, into the semi-finals.
Top seed Serena Williams, playing with a strapped left knee, claimed the last quarter-final spot after staving off Lucie Safarova's challenge with a 6-1 1-6 6-2 win that came in about an hour and half hours.
She meets Samantha Stosur in the quarter-finals after the Australia beat Alize Cornet 6-4 6-2.
(Reporting by Amlan Chakraborty in New Delhi; editing by Patrick Johnston)
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