The invention discloses a method and a device for coding and decoding. The method for coding and decoding comprises steps that a bit stream with preset length is acquired, and the bit stream is divided into K layers; K/2-layer code elements of the K layers are coded through a BCH code, and the K/2-layer code elements after coding are outputted; the residual K/2-layer code elements are coded through an LDPC-CC code, and the residual K/2-layer code elements after coding are outputted; modulation is carried out through a star-shaped QAM modulation mode, and modulation signals are outputted; the decoding method comprises steps that the modulation signals are acquired; the modulation signals are demodulated and outputted; demodulation signals of the K/2 layers of the K layers are decoded in a hard decision decoding mode, and the code elements after decoding are outputted; the demodulation signals of the residual K/2 layers are decoded in a soft decision decoding mode, and the code elements after decoding are outputted; the code elements after decoding are merged and outputted and are reduced to be the bit stream with preset length. Through the method, complexity of a coding and decoding system is reduced, integral coding and decoding efficiency is improved, and an error code rate is reduced.