In response to the lack of connected greenhouse plant protection spraying machines, low precision in mechanical straight-line positioning and rail switching, a segmented and variable distance spraying robot was designed for multi-span greenhouses to achieve unmanned spraying while improving operational precision. To meet the requirements of combining road and track operation and precise switching for mechanical operations in multi-span greenhouses, a universal mobile chassis was proposed with its key design parameters determined. To reduce deviations during chassis movement along the upper and lower rails, a rail correction device was designed. Through analysis, calculations, and experimental validation, an installation clearance of 4mm was established as suitable. Considering the significant chassis tracking errors, a road surface key point positioning and steering control method combining QR codes, gyroscopes, and photoelectric sensors was proposed. The design of the segmented and variable distance spraying device involved proposing a screw slide table-driven spray boom with variable-distance capabilities. The driving parameters were analyzed and validated to meet the operational requirements. Additionally, an auxiliary anti-vibration device based on roller bearings was developed to reduce damage caused by severe vibration of the spray rod. The chassis motion and segmented and variable distance spraying control system were developed to enable full automation of the spraying robot within multi-span greenhouses. Finally, performance and spray effect tests were conducted on the prototype, yielding the following results: the average straight-line travel error and tracking error of the chassis were 4.8mm and 5.8mm, respectively, meeting the requirements for control precision. The obstacle avoidance distance was 34cm, ensuring safety. The installation of the anti-vibration device reduced the vibration in the travel direction of the spray rod from -1° to 1.3° to within ±0.4° and limited the vibration in the nozzle direction from ±0.5° to within ±0.3°, demonstrating significant improvement in anti-vibration effectiveness. Following segmented and variable distance spraying, the deposition of mist droplets on the front surface of tomato leaves during the fruiting stage was approximately 1.76μL/cm2, while the back surface achieved approximately 0.2μL/cm2 of deposition. The mist droplet volume median diameter ranged from 100μm to 180μm, meeting the operational requirements.