The gaps and steps between platforms and trains reduce the accessibility and mobility of persons with wheelchair in railway transportations. Using an experimental platform, the observations were performed how gaps and steps influence their capabilities for wheelchair users with spinal cord injuries. A quantity of Normalized Driving Force (NDF) was introduced to evaluate the abilities of getting on/off trains. Dynamic wheelchair driving force was measured by using torque meter equipped on the wheelchair to analyze the power boarding on trains. To improve practical accessibility of persons with wheelchair, an assistive device for boarding trains was designed and verified.