This study examined the effects of dietary energy source and level on feed intake, digestion, rumen microbial protein synthesis and milk performance of lactating dairy cows fed corn stover as the main forage source. Eight primiparous Chinese Holstein cows (138 ± 19.4 DIM, 29 ± 0.8 kg/d milk, and 589 ± 57.6 kg of BW), 4 of which were fitted with ruminal cannula, were used in a replicated 4 × 4 Latin square design with a 2 × 2 factorial treatment arrangement (energy level: NE_L 1.52–1.53 Mcal for LE and 1.71–1.72 Mcal for HE; energy source: SFC and GC). The NE_L was calculated based on Chinese recommendation (2004). Changes to dietary energy level were induced by feeding the cows diets of either 35.6% corn stover plus 1.24% EB100 or 13% corn stover, 22% corn silage plus 1.84% EB100 (a saturated free fatty supplement). Milk yield [27.8 vs. 24.6 kg/d (0.45 SEM), P = 0.007], milk protein content and yield [0.86 vs. 0.76 kg/d (0.01 SEM), P = 0.006], and milk lactose yield [1.34 vs. 1.20 kg/d, (0.02 SEM) P = 0.008] increased in response to increased levels of dietary energy, while contents of milk fat [4.22 vs. 4.24% (0.06 SEM), P = 0.433]and milk lactose [4.94 vs. 4.90% (0.08 SEM), P = 0.323] were not affected. Cows fed HE diets had a higher microbial protein yield [1.57 vs. 1.34 kg/d (0.54 SEM), P = 0.003] than those fed LE diets. Apparent digestibilities of nutrients were higher in HE than in LE diets. Milk yield [25.8 vs. 23.3 kg/d (0.434 SEM), P = 0.047], milk protein yield [0.79 vs. 0.72 kg/d (0.02 SEM), P = 0.043] and microbial protein yield [1.42 vs. 1.25 kg/d (0.33 SEM), P = 0.038] were also higher when SFC was used to replace GC as the main energy source for lactating cows fed with LE diets. This study suggest that increased dietary energy level and ruminal degradation rate are beneficial to milk protein production when cows are fed corn stover as a forage source, and this can be attributed to the resulting increased supply of microbial protein.