The present disclosure provides optimized coding and decoding methods for polar codes and corresponding encoder and decoder. The coding method comprises: providing to-be-encoded input bits that include free bits and remaining bits; dividing the remaining bits into a plurality of fragments; providing a connection code; connecting one fragment of the remaining bits to the connection code to thereby form a connected fragment, while the remaining being still unconnected fragments; performing polarization coding to the free bits, the connected fragment, and the unconnected fragments to obtain the polar codes.