A new adaptive variable neural network is developed according to the inner product feature of sample space.This method does not need to iterate learning.It features that its self-learning velocity is fast

accuracy is high

and it is able to change self-structure on work according to producing new sample.It has been applied to a type of aeroengine start system

its accuracy of failure diagnosis is prior to the original one

and the maintenance work is cut down.Moveover it has capability for real-time failure diagnosis

which opens up bright prospect for its propagation.