Planting grass under forest is an under-forest economic model commonly used in plantations in recent years. In the forest and grass planting model, it is difficult to harvest forages and labor intensity caused by narrow tree spacing, lush vegetation, uneven ground, and limited visibility. A crawler-type forest grass belt harvester was developed. Its main features were small width, flexible turning, strong ground surface adaptability and low ground pressure. It was suitable for harvesting forest grass and cutting hard weeds and sparse shrubs. Through literature analysis and field investigation, four design requirements based on the working environment in the forest was put forward, so as to analyze the walking system, cutting system and supporting frame of the harvester. The specific ground pressure of the harvester was calculated, the cutting trajectory of the cutter and the motion state of the forage after being cut was analyzed, and the force state and deformation of the frame under special working conditions was analyzed through a combination of theoretical calculation and simulation analysis. And the dangerous section of the frame was found and the structure of the frame was strengthened to ensure the safety and reliability of the harvester. According to the standard arrangement test of the forage harvester, the operating speed of the harvester was 0.42m/s, the cutting height was 7.6cm, and the cutting width utilization factor was 0.94. The results show that the crawler-type inter-forest grass belt harvester can adapt to the operating environment under the artificial forest, and it can be used for forage harvesting in the small-distance forest and grass planting mode, which can reduce the labor intensity of artificially harvesting forage.