The theoretical solution for a Multiple-Degree-Of-Freedom (MDOF) structure is composed of a combination of several individual modes. When we demonstrate the actual response directly on the time-frequency spectrum, the energy distribution is usually concentrated at some range of frequencies, with the temporal variations of each band clearly shown. Those variations in the frequencies are the actual structure performances even though those "modal behaviors" are not coming from the theoretical solutions. Using the Hilbert-Huang Transform (HHT) the modal behaviors can be obtained easily by directly reading the time-frequency spectrum. To find Structural-Health-Monitoring (SHM) information, some numerical steps are found helpful. Including the signal enhancement skills, the time-frequency domain amplification function (T.F.AF), the modal temporal variation curve (MTVC) and the instantaneous frequency application. We develop a new method called the HHT SHM method; both experiment measurement and building observation are used to show the performance and method-validation. The procedures are described as follows. The original signal is first transferred into the wave-propagating properties, the T.F.AF. The T.F.AF can give dynamic parameter results through all phases in an earthquake event. After adopting useful modal information from the T.F.AF, which is called the MTVC. The MTVC contains detailed SHM information that enables observers to read the modal behavior. This is a new way to explore SHM information from actual records. These MTVCs can be used to explore the vivid differences in structure healthy conditions that might be ignored by other observers.