The invention provides a device for processing the frequency domain of a GNSS reflected signal and method thereof. The device comprises a receiving antenna, a radio frequency module, a signal processing module and an application processing module. The information of the direct projection signal and each multidiameter component such as code time lag and carrier frequency, phase are evaluated by cumulating the signal containing the reflected signal and spectral mapping and frequency domain analysis. The evaluated component of the multidiameter component can be used for use of the reflected signal, such as measuring the height using reflected signal, measuring the sea breeze. In view of tracking the direct projection signal from the receiver, the multidiameter component can be differentiated and eliminated, therefore the receiver can ease the influence of the multidiameter on code and carrier wave at the condition of the closed close range multidiameter. When the system changes, the structure of the signal processing module is constant and the parameter is adjusted to track and process the signal and the effective solution plan is provided to use and eliminate the multidiameter.