Background: Insufficient vastus medialis (VM) activation and excessive patellofemoral joint loading are primary contributors to patellofemoral pain (PFP). Although electrical muscle stimulation can reduce pain and enhance strength, evidence for its efficacy in selectively strengthening the VM and improving lower-limb biomechanics in PFP patients remains limited. This study aimed to investigate the clinical efficacy of electrical stimulation combined with strength training versus conventional strength training in PFP patients. Methods: Forty-six participants were randomly assigned to an electrical muscle stimulation combined strength training (EMS) group and a muscle strength training (MST) group. Both groups completed a 6-week hip/knee strengthening program (3 sessions/week, 60 min/session) whereas the EMS group received the extra electrical stimulation of VM during the knee training. Prior to and after the intervention, participants performed stair descent and isokinetic strength tests. Subjective knee pain and functional capacity were assessed using patient-reported measures, while kinematic, kinetic, and surface electromyography data were collected during stair descent. Results: After the 6-week intervention, both groups showed reduced knee valgus angle, hip internal rotation angle, patellofemoral joint stress and reaction force, along with decreased activation of the gluteus medius, gluteus maximus, and vastus lateralis and increased VM activation during stair descent (all p < 0.05). In addition, both groups exhibited increased hip and knee muscle strength (all p < 0.05). Compared with the MST group, the EMS group demonstrated greater improvements in medial-lateral quadriceps activation ratio and knee extension strength, alongside more reductions in knee external rotation angle, hip adduction angle, and the anterior knee pain scale scores (all p < 0.05). Conclusions: EMS combined with strength training more effectively mitigated abnormal hip–knee movement patterns during stair descent, balanced the activation of the vastus medialis and lateralis, increased knee extensor strength, and alleviated pain and enhanced function in PFP patients. Trial registration: Trial Registration Number: ChiCTR2300067598, Date of trial registration: 1/13/2023.