The hosts triumphed by five wickets with 14 balls to spare as they made light of chasing down a target of 118.
Sarah Taylor anchored the England reply with an unbeaten 52 off just 50 balls, while captain Claire Taylor weighed in with 21 off 13 deliveries.
Caroline Atkins’ unbeaten 20 - also at quicker than a run a ball - helped wrap up victory, a day after England won the opening encounter by 20 runs.
England’s performance in the field was equally impressive, Lynsey Askew and Laura Marsh sharing four wickets as New Zealand were bowled out for a below-par 117 in 18.1 overs.
Jenny Gunn, Holly Colvin and Beth Morgan claimed a wicket apiece in an innings that also saw three run-outs.
The sides meet again in the final Twenty20 international at Taunton on Thursday.