An improved extension method based on protograph extrinsic information transfer (PEXIT) charts is proposed to design rate‐compatible quasi‐cyclic low‐density parity‐check (QC‐LDPC) codes with more flexible rates and better performance. The masking matrix of the highest‐rate code can first be constructed column by column to own the lowest decoding threshold. Then, an extension algorithm is proposed to obtain the masking matrices of lower‐rate codes with flexible rates. Finally, the base matrices with small amount of short cycles are designed and the parity‐check matrices of rate‐compatible QC‐LDPC codes are obtained through matrix extension. Simulations show that compared with the existing codes, the proposed codes have more flexible rates while achieving better performance.