In this study, we developed the first two pairs of B,N-hetero[8]helicenes enantiomers (BN[8]H-ICz and BN[8]H-BO) through polycyclization decoration of a BN-MR emitter with an MR donor and acceptor group, respectively. The decoration group was found to alter the electronic charge distribution and thus affecting the helicity of helicene from a viewpoint of electronic structures, which determines the luminescence asymmetry property of helicenes rather than the geometric structure. Benefiting from its larger helicity of hetero[8]helicenes electronic structure, BN[8]H-BO showed a nearly one-order-of-magnitude higher glum and even higher luminance efficiency compared with BN[8]H-ICz, which only possessed a hetero [6]helicenes electronic structure. Consequently, BN[8]H-BO exhibits large glums of +2.75/-2.52 ⅹ 10 -3 , a high photoluminescence quantum yield (PLQY) of 99%, an emission maximum of 538 nm with a small FWHM of merely 34 nm simultaneously. Notably, the emission of BN[8]H-BO is narrower than most BN-MR helicenes. The corresponding device showed an electroluminescence dissymmetry factors (gEL) of +5.23/-5.07 ⅹ 10 -3 and a high external quantum efficiency of 31.7%, which remains 31.0% at practical luminance of 1000 cd/m 2 . What deserves to address is that the same devices showed an extremely long LT95 (time to 95% of the initial luminance) of over 731 h at an initial luminance of 1000 cd/m 2 . To the best of our knowledge, it is the first time that a green CP-OLED could achieve such a long lifespan. Our work not only provides B,N-hetero[8]helicenes with a high glum, narrowband emission, and good stability but also firstly points out the crucial importance of determining the real helicity of helicenes from the point of electronic distributions, which holds significant implications for the development of CPL emitters with enhanced chiroptical properties.