The present invention discloses an encoding method and device for Low Density Generator Matrix Codes (LDGC). Wherein, the method comprises: construct an LDGC mother code set using a plurality of LDGC with code rate R0 and different code lengths, wherein the LDGC mother code set has a uniform base matrix Gbuniform={(gi,jb)uniform}kb×nb; obtain length L of an intermediate variable according to a relationship between length K of an information bit sequence to be encoded in the LDGC mother code set and length L of the intermediate variable; obtain an expanding factor z for processing the base matrix using the length of the intermediate variable and the number of rows in the base matrix; process the base matrix using the expanding factor to obtain a binary generator matrix Gtmp, the front L rows and front L columns of which compose a triangular matrix; modify the binary generator matrix to obtain a modified binary generator matrix; take a matrix Gldgc composed of L rows and the front N+L−K columns of the modified binary generator matrix as a generator matrix of the information bit sequence to encode the information bit sequence.