Based on “Bilang”–200Y rape combine harvester header, four kinds of stalk separator including dustpan shaped separator, separator with side seed collection device, grid type separator, active arm-driving separator have been designed to reduce rapeseed losses in the process of mechanical harvesting. The results of field experiment showed that the separator with side seed collection device showed high resistance in the work process, causing the phenomenon of lateral pressure and hanging branches, which pose difficulty to achieve the separation of rape stem; the dustpan shaped separator could separate the rape stem, but the place where the stem inserted was too wide, causing unsatisfying stem insertion, besides, the stem could rebound; active arm driving separator could separate rape stem with no rebound. The loss rate of rapeseed using separator with side seed collection device, dustpan shaped separator, grid type separator and active arm-driving separator were 4.1%, 3.7%, 3.6% and 3.2% respectively. The results indicate active arm-driving separator, which showed the least loss rate of rape seed, is the ideal device for separation of rape stem.