Purpose <p>To evaluate and compare the efficacy of a newly designed in-house assistive internal fluid circulatory device in ureteroscopic lithotripsy for ureteral stones.</p> Methods <p>In this study, 97 patients were assigned to the trial group and underwent ureteroscopic lithotripsy with an in-house newly designed assistive internal fluid circulatory device; 96 patients were assigned to the control group and underwent traditional ureteroscopic lithotripsy without the assistive device. The primary outcome was the final stone-free rate (SFR) at 1-month post-surgery. Secondary observations included the quality of the surgical field, difficulty experienced during insertion of the ureteroscope, stone migration rate, operative time, change in serum creatinine, changes in the urinary leukocyte count, and perioperative complications.</p> Results <p>No significant differences were detected between the two groups in terms of gender, age, body mass index, location, or stone burden (<i>P</i> &gt; 0.05). At the 1-month follow-up, the SFR was significantly higher in the trial group than the control group (<i>P</i> &lt; 0.05). Furthermore, the operative time was significantly shorter in the trial group (<i>P</i> &lt; 0.05) with easier ureteroscope insertion relative to the control group (<i>P</i> &lt; 0.05). The incidence of stone migration in the trial group was significantly lower than that in the control group (<i>P</i> &lt; 0.05) and the quality of the surgical field was significantly improved (<i>P</i> &lt; 0.001). No significant differences were detected in terms of serum creatinine levels, urinary leukocyte counts, or perioperative complications (<i>P</i> &gt; 0.05).</p> Conclusions <p>The application of an assistive internal fluid circulatory device represents an effective and safe method for ureteroscopic lithotripsy.</p>