Intramedullary nail (IMN) is one of the key essential minimally invasive "weapons" in orthopaedic trauma, while the distal locking is still challenging for surgeons. Although there are various inventions and technologies to improve the locking procedure, there are still problems such as inaccurate positioning, excessive radiation exposure, low first success rate and long learning curve. Therefore, a new laser guiding navigation device was designed and compared with the traditional freehand (FH) technique in the distal locking of femoral IMN.This randomized controlled single-blind trial recruited patients with femoral diaphyseal fracture. The self-designed laser navigation device (laser group) and freehand technique (FH group) were used in the distal locking of the IMNs. The patients enrolled were randomized into FH group and laser group, all operations were performed by two surgeons of the same level. The differences between the two groups were compared in terms of radiation exposure time, operative time, first success rate, blood loss, visual analogue score (VAS), Harris score and healing time.32 patients ended the study period and 16 patients in each group. The results showed that the laser group was better than the FH group in terms of distal locking time (10(9/11) vs 19.5 (17.25/21) min, Z = 4.83, P < 0.001), distal locking radiation exposure time (46.5 (41.25/51.75) vs 105 (88.25/140) s, Z = 4.807, P < 0.001), first success rate (30/32 vs 20/32, χ2 = 9.143, P = 0.002) and blood loss (60 (50-100) vs 150 (105-192.5) mL, Z = 3.610, P = 0.0003). There was no difference in Harris score, VAS score, or fracture healing time between the two groups.Compared with the FH technique, the novel laser guiding navigation device for distal locking of femoral IMN has the advantages of shorter operative time, less radiation exposure and higher first success rate. Trial registration Chinese Clinical Trial Registry, ChiCTR2200060236. Registered 23 May 2022, https://www.chictr.org.cn/showprojen.aspx?proj=169130.© 2022. The Author(s).