Abstract: In this trial, effects of N fertilizer amount, P fertilizer amount and plant density to crude fiber of grain and forage maize in different harvest periods were studied, applying 3 factors optimum saturation designing. It showed crude fiber contents in all organs increased from the scattering stage to the milk stage. Crude fiber content was higher in stems and it had no much difference in leaves and spikes. With the increase of N, P and density, the crude fiber accumulation were dropped in leaves, stems and spikes, and the accumulation in spikes was lower in middle treatment of density and N and P amounts. From nutrient angel, the best harvest period is end milk stage, and the suitable density is 5200~5700 plant/hm2, the suitable N and P amounts were 270~350 kg/hm2 and 100~140 kg/hm2 in Hohhot.