I. Introduction
As the critical technique of prognostic and health management(PHM), remaining useful life(RUL) estimation plays an important role in the predictive maintenance of large equipment, which aims at estimating the performance of machinery across its lifetime period, and providing a suitable maintenance plan to avoid serious accidents occurring. With the development of the Internet of Things(IoT) and industrial digitalization, the current industrial systems have been gradually turned to become a data-rich environment. These changes have created an unprecedented opportunity to research and develop the advanced RUL method and application by the powerful deep learning technique [1].