The Hilbert energy spectrum's principle in HHT is analyzed in the paper; Aimed to solve the end problem in the instantaneous spectrum figure, the cause is researched and ARMA model is introduced in the calculation of Hilbert of HHT. By the simulation of several typical IMFs about vibration signal of rotating machine, and comparing with the conventional methods, the advanced method is proved to be able to improve the end problem effectively and optimize the Hilbert energy spectrum greatly.