To understand the generation of temperature nonuniformity and its influence on effective emissivity, a radiant characteristics calculation method based on Monte Carlo(MC) full ray tracing technique for V-grooved surface blackbody is proposed. The exactitude of this method is approved by comparison with precise Bedford method, then the reason and development of temperature nonuniformity are discussed, and finally the effects of temperature nonuniformity on effective emissivity are disclosured. The results demonstrate that the temperature uniformity is deteriorated when small grooved angle, high grooved length and big temperature difference between surface temperature and environment are adopted. Further more, the grooved angle and length can exert influences on effective emissivity. It is concluded that the grooved angle of 45° of 60° and the grooved depth less than 2 mm can give a satisfied effective emissivity and temperature uniformity to general application. Better performance can be achieved when heat pipe technique and guarded sleeve are applied.