According to the environmental and production requirements of regions such as the NCP, we proposed an intercropping system of alfalfa and silage corn in which (i) alfalfa is harvested as hay in spring, (ii) interseeding silage corn into the alfalfa stand while alfalfa serves as ground cover during summer, (iii) a mixture of corn and alfalfa is harvested in the autumn for use as silage [7]. Previous papers published from the study of this new system reported the system productivity, influences of interspecific competition and the benefits achieved from the agronomic, environmental and economic points of view [14; 15]. It has been shown that the alfalfa-silage corn intercropping system was advantageous in promoting the overall forage production, and the alfalfa production during spring was not affected. Furthermore, we want to evaluate the system performances during summer, especially for the influences of intercropping on the silage quality. Many studies focused on the influences of an appropriate legume-grass ratio in the silage mixtures on the silage quality [13; 16], and they showed that the alfalfa-silage corn mixtures improve silage crude protein (CP) content and in vitro digestibility which leads to higher feed intakes and milk production compared with corn silage alone [17; 18; 19]. However, the effects of ground cover companions and the field managements on silage mixtures are seldomly mentioned. Previous studies have shown that perennial ground covers can lead to a yield reduction of 10-23% in silage corn [10; 20], while the appropriate N application improves corn yield and its CP concentration, especially in intercropping with the strong competitor alfalfa [2; 14; 21]. Increasing corn plant density has a positive effect on the silage yield of corn but negatively affects the alfalfa stands, which is shade-intolerant, for the limiting of light transmittance [22; 23]. Therefore, the N application rate and corn plant density have further effects on the alfalfa and silage corn ratio, nutritive values, and fermentation characteristics of the mixed silage. The winter wheat (_Tritcium aestivum_ L.) and summer corn rotation has been the most popular cropping system in the NCP since the 1970s [24]. In this study, to better evaluate the advantages of the alfalfa-silage corn intercropping system in production performances during summer, the monoculture silage corn managed according to local farmers' practices, which could represent the local production levels, was set as a control. A 2-yr experiment was conducted to examine the effects of intercropping, the N rate and corn plant density on the yield and N accumulation of both alfalfa and corn, as well as on the fermentation quality and chemical composition of the corresponding silage mixture products. We hypothesized that: (i) intercropping would decrease system yield while increasing the crude protein yield, (ii) N application would improve the yield and CP content of the intercropped corn but decrease the alfalfa yield, and it would improve CP content of the mixed silage, and (iii) a high corn plant density had a significant negative effect on alfalfa growth as well as silage quality. The objectives of this study were to identify whether the improvement of silage quality could compensate for the yield loss of silage maize in intercropping compared with local farmers' practices and to explore the appropriate field management methods to improve system yield, nutritive value, and ensilability.