An improvement of histogram-pair based image reversible data hiding by using RZL (Reverse Zero-run Length) coding is proposed in this paper. The pre-processing to compress data to a shortest one is usually adopted for raising the PSNR (Peak Signal to Noise Ratio) in data hiding. Recently, the disagreements appear that we can get better PSNR by using RZL coding after compression. We proved that our histogram-pair based image reversible data hiding is suitable to use RZL to improve the performance. The PSNR can be raised by using different RZL methods, different parameters, different embedded capacity and different images. It is hard to apply RZL to given original data with different lengths. We proposed a method to solve that by adding some 0 s to the original data to form a complete block, and the RZL needs an attached mark for lossless recovery. In our experiments it has been shown that the PSNR of image with histogram-pair based reversible data hiding by using RZL is higher than that without using RZL as the embedding data rate is not high. Zhang et al.'s RZL is better than Wong et al.'s in most cases. The average PSNR gain is about 1 dB for five test images at different payloads with the RZL used in this paper.