To investigate the effects of nitrogen application and harvest time on summer maize grain filling and dehydration, yield formation, and nitrogen use efficiency in thermal resource restricted area in the North China Plain, we adopted a two-factor randomized block area experiment design, one factor was nitrogen application rate per hectare [0 kg (N0), 120 kg (N120, 2021), 180 kg (N180), 240 kg (N240), 300 kg (N300), 360 kg (N360), and 450 kg (N450, 2020)], and another factor was harvest time [normal harvest (NH) and delayed harvest (DH)]. Dry matter accumulation (DM), grain filling and dehydration processes, grain yield (GY) and its components, nitrogen partial factor productivity (PFPN), and agronomic nitrogen utilization efficiency (ANUE) were investigated. Compared to the dry year (2020), DM, grain weight (GW), a%, respectively, resulting in GY, PFPN, and ANUE significantly reduced by 31.4%-58.3%, 27.2%-30.0%, and 2.9%-18.0%, respectively. Compared with N0, nitrogen application significantly enhanced DM, and GW were 14.6-82.1 mg grain-1 higher than N0, while the maximum grain filling rate (Gmax) and its weight increment (Wmax) were enhanced by 0.2-3.4 mg (grain d)-1 and 10.4-44.1 mg grain-1, meanwhile the time reaching Gmax (Tmax) were earlier by 0.4-7.0 d. The GY of nitrogen application treatments were dramatically raised by 51.5%-169.5% than N0, and in the N240 level it was the optimized nitrogen application. Compared with that of N180/N120, with the increase of nitrogen application rate, the PFPN and ANUE in two years were significantly reduced by 11.7%-57.9% and 2.5%-54.9%, 19.9%-52.6% and 4.9%-37.0%, respectively. Compared with NH treatment, the DM and GW of DH treatment were increased significantly by 0.8%-55.7% and 3.4%-79.3%, and dramatically reduced grain moisture content to 22.0%-27.9% at harvest stage. The GY, PFPN, and ANUE of DH treatment were remarkable higher than NH treatment by 10.6%-18.5%, 4.4%-26.8%, and 1.5%-48.6%, respectively. The linear plus platform model showed that the highest GY of DH treatment obtained to 12.0×103 kg hm-2 and 7.0×103 kg hm-2, which were significantly higher than NH by 11.3%-12.6%, whereas the optimal nitrogen application rate were reached to 247 kg hm-2 form 200-210 kg hm-2, increased by 13.9%-22.9%. In conclusion, in thermal resource restricted area in the North nd ear grains number (EGN) under rainy year (2021) were significant decreased by 16.3%-81.5%, 2.1%-28.1%, and 44.7%-47.4 China Plain, the nitrogen application rate could reduce to 200 kg hm-2 and GY stabilized above 6.0×103-10.5×103 kg hm-2 under normal harvest time, meanwhile the nitrogen application rate could optimized to 240 kg hm-2 and achieved higher GY above 8.0×103-12.0×103 kg hm-2 with higher PFPN and ANUE at 19.2-49.6 kg kg-1 and 15.2-20.8 kg kg-1 levels under delayed harvest. In conclusion, the results revealed that the theoretic support for reduced summer maize grain moisture content, achieving the production goal as grain machine harvesting, nitrogen reduction, high yield and high nitrogen use efficiency of summer maize in the North China Plain.