By numerically solving the time-dependent Schrdinger equation, we investigate the ionization probability, photoelectron spectrum, and harmonic emission spectrum of the atom under the action of high-frequency laser pulses. It is found that with the increase of incident laser pulse intensity, the ionization probability of the atom first increases to a maximum value gradually and then decreases, and in this process, both the photoelectron spectrum and high-order harmonic generation spectrum change from a single-peak structure to a multi-peak one. Through the time-frequency analysis of the harmonic emission spectrum, we also find that the harmonic emission is suppressed around the pulse peak, and it occurs at the rising edge and the falling edge, which interfere with each other, thus forming the multi-peak structure. Utilizing the laws of the changes of photoelectron and harmonic spectra with incident laser pulse intensity, we can diagnose the laser intensity at which the atomic ionization suppression occurs.