Abstract: The Signal to Noise Ratio （SNR） of GPS satellites beacon is mainly influenced by the gain of GPS satellites transmitter and receives on the ground, the geometrical distance between GPS satellites and receives, the elevation of the receives and the ionosphere medium attenuation. In this paper, a method is proposed to separate ionospheric attenuation from the observation of SNR. The technique was used to analyze the data observed at MANA station （273.751°E, 12.149°N） in 2003, and to construct a mean diurnal change pattern of the ionosphere medium attenuation. Comparing with the attenuation value calculated using IRI. It shows that the result fits with IRI well in the change of the attenuation value of SNR with the local time, when GPS signal radio vertically penetrates through the ionosphere.