Xen Hardware-Assisted Virtualization(HVM) is a service that one can run a virtual machine which is a unmodified OS on Xen Hypervisor. HVM causes a loss of management of the process granularity for the reason of VMM's lack of interference and understanding of the guest OS. This paper presents a lightweight process trace method for Xen HVM named Xen HPT. With the assistance of guest OS register information (mainly the ESP) collected by VMM, Xen HPT can implicitly capture the real-time process information of target guest OS outside on Domain0 with little effect on guest OS.Xen HPT has been tested by Linux guest OS and result shows that the method is effective.