To acquire better flattening performance of the alfalfa cutting and flattening machine, a kind of test bench was proposed. According to alfalfa flattening impact factors, including flattening gap and velocity, alfalfa growth, machine walking velocity and so on, the flattening device, drive system and data acquisition system have been designed. The multi-factors orthogonal test for alfalfa flattening was executed by changing the flattening roll gap, flattening roll rotational speed and feeding rate on test bench. The results of validity test showed that the pressure values between flattening rolls showed a regular change, and the most significant impact factor of the nutrient content of alfalfa is the spreading quantity, followed by the roll gap, feeding rate and roll rotational speed. This alfalfa flattening test bench can simulate the actual operation effectively, and provide the guidance of alfalfa cutting and flattening machine design.