Abstract: Under conventional tillage, we studied the effects of fertilization and planting density on maize protein content, in order to find out the cultivation theory basis that enhances the maize protein content. Quadratic orthogonal regressive rotation design with five factors was applied to studying the relationship between protein content of maize in 2013 and fertilization and density through wheat-maize rotation, thus to put forward the control measures. The results showed that if other factors were in medium level, protein content firstly increased and then decreased with the increase of nitrogen fertilizer or organic manure, but firstly decreased and then increased with phosphorus fertilizer increase, and showed a gradual linear rise with the increase of potassium fertilizer and planting density. The effect of nitrogen fertilizer on protein content of maize reached a very significant level, the effect of organic manure reached a significant level, but the other factors did not influence significantly. Certain significant interactions occurred between the rate of organic manure and planting density, and between the amount of nitrogen fertilizer and the amount of potassium fertilizer, but no significant interaction was found between the other experimental factors. It indicated that overusing nitrogen fertilizer and organic manure could not benefit the protein content of maize, but rational supply of P and K fertilizer and increasing planting density could get a higher protein content of maize.