In order to figure out the different temporal and spectral characteristics between two earthquakes with close hypocenter and short time interval in the same seismic sequence, two main shocks，MW 6.4 and MW 7.1 among the 2019 Ridgecrest earthquakes at California USA in July are selected. The attenuation trend of ground motions parameters with the change of epicentral distance for these two earthquakes is compared with Yu's model. The difference of three key elements of ground motions between these two earthquakes，including peak ground acceleration, response spectrum and duration，are analyzed. The potential seismic damage to structures is discussed by the response spectrum analysis of the selected two severest ground motions. The Hilbert-Huang transform（HHT） is adopted to obtain the HHT spectrum of ground motions for identifying the energy distribution in temporal and spectral domains. It shows that the attenuation trend of most of data agrees with Yu’s model. The response spectra of the two earthquake events are similar. The instantaneous frequency corresponding to the largest energy of HHT spectrum is close to peak-trough frequency corresponding to the time series cycle with peak ground acceleration. Structures may be severely damaged subjected to two earthquakes occurred successively.