Based on the COSMIC occultation data from 2007 to 2012, combined with the improved refractive breakpoint method, the seasonal and diurnal variation characteristics of the global maritime boundary layer height were analyzed. Fourthermore, the analysis results were also evaluated by sharpness coefficients. High boundary layer approximately distributes in an asymmetric zone, and in several regions of the low and middle latitudes there is the highest boundary layer, the height gradually decreased from the equator to the north and south poles. In some regions covered by the subtropical high, the seasonal variation of boundary layer height was not obvious, while in the area of the west coast of the mainland where the stratiform cloud is prevalent, there is some seasonal variation characteristics.The diurnal variation of the boundary layer height is relatively weak and is slightly different in different areas. The evaluation of the sharpness coefficients shows that the largest sharpness coefficient appears in the subtropical zone, and the refractive breakpoint method can provide accurate boundary layer height in the area, while in the equator convergence zone and the South Pacific convergence zone, the minimum sharpness coefficient makes the definition relatively fuzzy.