A decoding method for low density generator matrix codes that decodes a received bit information sequence that is transmitted after encoding with LDGC, comprising: S1: filling L-K known bits in a received code word sequence R and deleting code word symbols erased by a channel in R, hence generating a sequence R e, wherein K is the length of original information bits, L is the encoded length of the original information bits after filling; S2: deleting rows corresponding to the code word symbols erased by a channel from a transposed matrix G Idgct of an LDGC generator matrix, and getting G e; characterized in that the LDGC generator matrix is a structured LDGC generator matrix; and by using WNum processing words to sequentially store part of the matrix elements of each row in G e after performing erasure and column permutation to the LDGC generator matrix, and each processing word is used for storing WWid matrix elements of G e; S3: obtaining I t according to relation G e ×I t = R e; S4: obtaining s t according to relation G Idgct (0:L-1,0:L-1)×I t =s t, and getting an original information sequence of K bits by deleting the filled L-K known bits from s t; the G Idgct is a GF field matrix of N+L-K rows and L columns, WWid is the word width of the processing word, WNum=ceil(P/WWid), and P is the number of matrix elements of each row in G e that are stored by using one bit of the processing word; wherein a square matrix corresponding to the first L rows in the G Idgct is a lower triangular matrix; step S3 includes the following substeps: S31: generating G a = A C D B by performing column permutation to G e, wherein A is an M-order lower triangular matrix, and recording corresponding relationship of column permutation between G e and G a; S32: obtaining I' t according to relation G a× I' t = R e, and getting I t by performing inverse permutation to I' t according to the corresponding relationship of column permutation; wherein the processing words are used for sequentially storing all matrix elements of each row in C and B, and each bit of each processing word is used for sequentially storing WWid matrix elements of C and B; wherein the M=L-X L, where X L is the number of bits erased by a channel in the first L code word symbols of R. S1: filling L-K known bits in a received code word sequence R and deleting code word symbols erased by a channel in R, hence generating a sequence R e, wherein K is the length of original information bits, L is the encoded length of the original information bits after filling; S2: deleting rows corresponding to the code word symbols erased by a channel from a transposed matrix G Idgct of an LDGC generator matrix, and getting G e; characterized in that the LDGC generator matrix is a structured LDGC generator matrix; and by using WNum processing words to sequentially store part of the matrix elements of each row in G e after performing erasure and column permutation to the LDGC generator matrix, and each processing word is used for storing WWid matrix elements of G e; S3: obtaining I t according to relation G e ×I t = R e; S4: obtaining s t according to relation G Idgct (0:L-1,0:L-1)×I t =s t, and getting an original information sequence of K bits by deleting the filled L-K known bits from s t; the G Idgct is a GF field matrix of N+L-K rows and L columns, WWid is the word width of the processing word, WNum=ceil(P/WWid), and P is the number of matrix elements of each row in G e that are stored by using one bit of the processing word; wherein a square matrix corresponding to the first L rows in the G Idgct is a lower triangular matrix; step S3 includes the following substeps: S31: generating G a = A C D B by performing column permutation to G e, wherein A is an M-order lower triangular matrix, and recording corresponding relationship of column permutation between G e and G a; S32: obtaining I' t according to relation G a× I' t = R e, and getting I t by performing inverse permutation to I' t according to the corresponding relationship of column permutation; wherein the processing words are used for sequentially storing all matrix elements of each row in C and B, and each bit of each processing word is used for sequentially storing WWid matrix elements of C and B; wherein the M=L-X L, where X L is the number of bits erased by a channel in the first L code word symbols of R. S31: generating G a = A C D B by performing column permutation to G e, wherein A is an M-order lower triangular matrix, and recording corresponding relationship of column permutation between G e and G a; S32: obtaining I' t according to relation G a× I' t = R e, and getting I t by performing inverse permutation to I' t according to the corresponding relationship of column permutation; wherein the processing words are used for sequentially storing all matrix elements of each row in C and B, and each bit of each processing word is used for sequentially storing WWid matrix elements of C and B; wherein the M=L-X L, where X L is the number of bits erased by a channel in the first L code word symbols of R.