Abstract: The gap between the mutual information of the Gray-coded amplitude phase shift keying ( APSK) and the channel capacity can not be narrowed sufficiently，especially with non-iterative independent demapping at the receiver，in order to solve the problem，a non-equiprobable APSK constellation is proposed． The mutual information under the restriction is improved by reducing the number of constellation points corresponding to the inner loop and transforming it into a low-order Gray-PSK． Simulation shows that the 64NE-APSK designed for 2 /3 code rate has a performance advantage of 0． 6 dB compared to the 64Gray-QAM constellation，having an advantage of about 0． 1 dB over the 64Gray-APSK． Therefore，in the case of independent de-mapping at the receiver，the design helps approaching the channel capacity without increasing the complexity of the system implementation．

Key words: non-equiprobable constellation mapping, channel capacity, independent demapping