∵△ABC是直角三角形,两直角边AC=6cm、BC=8cm,
∴AB=
A C 2 +B C 2 =
6 2 + 8 2 =10,
∵△ADE由△BDE折叠而成,
∴AE=BE=
1
2 AB=
2 ×10=5cm.
故答案为:5.