Simmonds qualified seventh fastest for the women's 200m backstroke final
Great Britain qualified for both the men's and women's 4x100m medley finals while David Davies and Lizzie Simmonds also booked final berths.
The British women set a new European record as they qualified second behind Australia while the men came third in their heat to set a new British mark.
Earlier, Welshman Davies qualified fifth for the men's 1500m freestyle.
Simmonds made it through to the women's 200m backstroke final but fellow Brit Gemma Spofforth narrowly missed out.
In the 4x100m medley relays, Britain's women posted a time of three minutes 59.14 seconds to qualify second, while the men set a new national record of 3:33.83 as they qualified fifth fastest.
I've made an Olympic final - it's the stuff you dream of
British backstroker Lizzie Simmonds
The United States went through as fastest qualifiers despite resting Michael Phelps.
"We just needed to get the 'A' guys in a good spot," said backstroker Matt Grevers, who led off the quartet.
"We got the job done, we had safe starts, that was the goal, safe starts, no DQ (disqualification) for no reason.
"We've heard those words a lot. I don't think we'll be allowed to leave China if we get a DQ."
In the women's 200m backstroke, Simmonds clocked 2:08.96 to qualify seventh fastest.
"It was tough getting up for that race after last night but I couldn't be happier with how it went," said Simmonds.
"I've made an Olympic final. It's the stuff you dream of. Anything can happen now, there are some tough girls in there so we'll have to see. I'm very excited."
Kirsty Coventry of Zimbabwe was the fastest into the final, winning the second semi-final in 2:07.76.
Elizabeth Beisel of the US won the opening semi ahead of Japan's Reiko Nakamura.
Olympic 100m freestyle champion Alain Bernard of France kept alive his hopes of a sprint double as he took his place in the final of the 50m event.
Brazilian Cesar Cielo Filho broke the Olympic record with a swim of 21.34secs in the other semi-final, while Australia's Eamon Sullivan came in third.
Fran Halsall was the eighth fastest qualifier for the women's 50m freestyle semi-finals.
Halsall, who was eighth in the 100m final earlier on Friday, clocked 24.93secs to finish behind fastest qualifier Cate Campbell of Australia and American veteran Dara Torres.
World record holder Libby Trickett and 100m champion Britta Steffen also progressed, as did Marleen Veldhuis of the Netherlands.