Aiming at the requirement of feasibility analysis for ice cloud detection by space borne cloud radar， the single scattering characteristics of non-spherical ice crystals to 340 GHz electromagnetic wave were analyzed， then the echo characteristics of non-spherical ice crystal cloud and dual wavelength ratio （DWR） of 94\340 GHz cloud radars were studied based on different volume scattering models， while the variation of DWR with altitude and the thickness of ice clouds that can be penetrated were discussed assuming the vertical distribution of ice clouds. Compared with 94 GHz and 220 GHz， the scattering ability of ice particles to 340 GHz electromagnetic wave is enhanced， but at the same time， the attenuation by clouds is also greatly increased， and the attenuation coefficient of ice clouds to 340 GHz wave is about 5~130 times that to 94 GHz wave. The 340 GHz cloud radar can detect the shallow ice clouds with low ice water content （IWC）， that is， ice cloud with thickness of 2 km and IWC of 0.000 1～0.2 g/m³ can be detected basically， and the electromagnetic wave penetration ability is greatly reduced due to the attenuation of thick clouds with more water content， when the maximum IWC reaches 1 g/m³ in the condition of the assumed vertical distribution of IWC， about more than 40% of cloud thickness for ice clouds within 5 km will be detected. Attenuation also results in different DWR for clouds with the same drop spectrum at different heights. The value and vertical distribution of IWC affect the value of DWR and the thickness of the clouds detected by electromagnetic wave. The attenuation increases with the increase of IWC and the electromagnetic wave attenuation of high frequency cloud radars is larger， that make the DWR larger， so the DWR is related to the number concentration of the spectrum. As a result， the attenuation correction is very important when using DWR retrieval.