Abstract: The distribution characteristics for the worst month period are important technical requirement for the design of radio communication systems. The reference statistics for many radio meteorological data and propagation prediction methods is the long-term average annual distribution, consequently there is a need for a method that provides for the conversion of the annual to the worst month statistics. The complete concept of the worst-month is proposed including cumulative distribution and complementary cumulative distribution. The conversion models of annual statistics to worst month statistics is analyzed for troposcatter transmission loss, rain rate, rain attenuation, and multipath propagation loss at line-of-sight links, and the parameters. The optimal model parameters are given through comparative analysis, and the root mean square (RMS) error corresponding to the optimal model parameters is the smallest, among which the RMS errors of tropospheric scattering and rain attenuation are less than 10%. Meanwhile, it is demonstrated that the conversion relationship of rain attenuation can be obtained from the conversion relationship of rain rate. The research herein will strongly support the worst month design of radio systems.