Aiming at the problems of complex structure，long transportation distance and block of chain scraper conveying groove on rape combine harvester，an integrated longitudinal axial flow threshing and separating device was designed，which could replace the traditional chain scraper conveying groove. The forced feeding unit and longitudinal axial flow threshing and separating device were integrated together，their axes were distributed as “T”pattern. Rape stalks were transported by forced feeding unit and threshed and separated relying on longitudinal axial flow threshing and separating device. According to the working process of integrated longitudinal axial flow threshing and separating device，length，diameter，and rotational speed of forced feeding wheel and longitudinal axial flow threshing cylinder and other main parameters were determined. The indoor experiment was conducted and its results showed that when the feed quantity was 2.0kg/s and rotational speed of forced feeding wheel ranged from 300r/min to 450r/min，entrainment loss rate of integrated longitudinal axial flow threshing and separating device was less than 1.31%；when the rotational speed of forced feeding wheel was 400r/min，and feed quantity varied from 1.0kg/s to 2.5kg/s，the entrainment loss rate of was less than 1.18%，which met the design target of threshing and separating device for rape. Field experiments on rape combine harvester showed that integrated longitudinal axial flow threshing and separating device could adapted to operational requirements of rape combine harvester，materials were transported from header to threshing and separating device evenly and successively and threshed and separated. This study provided a reference for simplifying the whole structure of the rape combine harvester and reducing the flow path of rape in the combine harvester.