The Dublin light-welter dropped a majority decision (40-36,38-38, 39-37) to the World No. 14 in a close encounter in Central Asia.
Harrington found the target with the majority cleaner shots over the four frames, but the judges favoured the up tempo approach of the No. 3 seed, who clipped Harrington with some neat counters, particularly in rounds two and three.
Harrington, switching stances, detonated the best shot of the fight in the third, a right hook, followed by another shot on the bell, but the judges split in favour of Wenlu, who tagged the Dubliner with a solid left in the fourth.
Harrington responded in kind going down the final stretch, but the decision went to the Asian Confederation champion.
Harrington and Katie Taylor claimed silver and bronze in Astana to mark the first occasion two Irish female boxers finished in podium positions at the same World Championships.
Taylor was beaten by France’s Estelle Mossely in the last-four. Mossely beat Russia’s Anastasiia Beliakova in yesterday’s final to become the first female boxer other than Taylor to win World 60kg gold since Russia 2005.
Harrington, meanwhile, will move into a top five position in the world 64kg rankings after picking up 800 points for silver.
She said: “Now I’m know I’m up there with the best and all I have to do is keep pushing.
“I believe because everybody here is making me believe. Next time I come here it will be gold I take home.”
Harrington won four of her five fights in Astanta and produced some memorable performances, but, alas for Irish sport, light-welter is not an Olympic weight.
Harrington is hoping there will be more Olympic weights for women at Tokyo 2020, and the President of the International Boxing Association (AIBA), Dr CK Wu, is in her corner.
He said: “Of course three categories (for women) is not enough.
“We need to increase the categories. In my mind, at least, we can work for the targeting of 2020 to have five categories, two more.”
Harrington, meantime, reckons her top two finish will grant her, literally, the chance to improve as an athlete.
“It means now I’m on funding. I’ll be able to train more. I’ll be over with the high performance lads, getting more great sparring,” said the fifth Irish boxer after Taylor, Michael Conlan, Joe Ward and Jason Quigley to reach an AIBA World Elite final.
Kazakhstan, China, USA, coached by ex Irish head coach Billy Walsh, France, Great Britain and Italy, in that order, commanded the top six places in the medals table in Astana, with Ireland, Australia and Bulgaria sharing 7th spot.
The final two qualifiers (for men) for Rio will be held next month and in July.
Team Ireland are due to arrive home from Astana at 9.50am this morning through Dublin Airport.