In order to improve the completely mechanical production level of hydroponic lettuce, an automatic packaging machine was designed and manufactured. It mainly contained guiding device, film cutting and covering device. The packaging machine could implement putting lettuce into packaging box lengthways and covering film automatically. The lettuce was put into the box by cylinders, and a guiding annulus was utilized to decrease lettuce excursion and reversal. The flexible brush combed the selfadhesive film on the box. The size of the packaging box, the parameters of guiding device, and the parameters of film cutting and covering device were confirmed by lettuce extrusion test, mechanical analysis and theoretical calculation, respectively. The influence of guiding annulus on lettuce position and posture characters, for instance the horizontal excursion and attitude angle, was analyzed by highspeed photograph. The packaging test results showed that the average value of horizontal excursion with guiding annulus was 5.8mm when lettuce entering the box, which was reduced by 75.0% than that without guiding annulus. The average value of attitude angle with guiding annulus was 17.9°, which was reduced by 74.2% than that without guiding annulus. The guiding annulus could ensure the success rate of putting lettuce into the packaging box. The optimized combination of film cutting parameters was obtained by orthogonal tests, and the angle between longitudinal cutter and film, film stretching velocity, and film transverse cutting velocity were 30°, 300mm/s and 500mm/s, respectively. The verification test results showed that the success rate of packaging was 96%, and the single packaging operation time of prototype was 10.5s, and it was reduced by 58% than that of manual operation.