Objective To study the effect of gradient Z-axis gain on magnetic resonance diffusion-weighted imaging (WB-DWI) image splicing. Methods A total of twenty patients with bone metastases confirmed by bone imaging were prospectively studied. WB-DWI was performed twice in each patient (SEQ 1 and SEQ 2). Where sequence 2 is adjusted only to -5 to 5 on the Z-axis gain relative to sequence 1, and the remaining parameters are consistent with sequence 1. Evaluate the two sequences to check for splicing image differences, and the difference of diagnostic rate between WB-DWI and PET-CT based on the results of bone scan. Results (1) The splicing image quality: 17 patients scored greater than or equal to 3 points with sequence 2 more than that scored greater than or equal to 3 points with sequence 1, and the difference was statistically significant (P<0.05). (2) The number of suspected bone metastases of sequence 2 was 78, which was higher than that of sequence 1 (65), the difference was statistically significant (P<0.05). (3) WB-DWI sequence 2 found that bone metastases were significantly higher than those in the control group (PET-CT), and the number of suspected bone metastases was 78, but there was no significant difference between the two groups (P>0.05). Conclusion WB-DWI has a good diagnosis and differential diagnosis of tumor-induced bone metastatic disease. It is helpful for WB-DWI image splicing and improving the image quality.