The 17-year-old swimmer from Walsall recorded a time of 3:08.14 in the 200m individual medley at the brand new Olympics venue in Stratford.
Competing at the British Gas Swimming Championships, she beat her personal best by over half a second.
Earlier this week she came second in the 100m freestyle after being beated by Beijing Gold medallist Heather Frederiksen
Speaking after the event Ellie said:
– Ellie Simmonds, Double Paralympic Champion
"I wanted to enjoy it and getting gold is great, but a world record is something else."
Sascha Kindred from Herefordshire also won the men's 200m individual medley race, with a time of 2:48.44.
To assure a place at this summers Paralympic games, all swimmers must compete at the British International Disability Swimming Championships in Sheffield next month