The inefficient utilization of nitrogen (N) fertilizer due to leaching, volatilization and denitrification has resulted in environmental pollution in rain-fed maize production in Northeast China. Active canopy sensor-based in-season N application has been proven effective to meet maize N requirement in space and time. The objective of this research was to evaluate the feasibility of using active canopy sensor for guiding in in-season N fertilizer recommendation for rain-fed maize in Northeast China and determine if the plant height information could be used to further improve the accuracy of in-season N recommendation. Nitrogen response trials were conducted in four growing seasons with four planting densities. Split plot treatments included six N application rates (0, 60, 120, 180, 240, and 300 kg ha-1) at each year-density with three replications. One third of the N was applied as basal fertilizer, and the rest as side-dressing at V8-V9 stage of spring maize. The GreenSeeker active canopy sensor was used at the 8-9 leaf growth stage (V8–V9) to collect the vegetation index (NDVI), which was used with the N fertilizer optimum algorithm (NFOA) to calculate in-season N fertilizer side-dressing rates. Plant height and yield were obtained at V8–V9 and harvest stage respectively. The results showed that both NDVI and NDVI*Height could predict the yield potential accurately. The NFOA recommended higher side-dressing N rates using NDVI*Height than NDVI. The average total N rate based on NDVI*Height-NFOA recommendation was closer to economically optimum N rate than based on NDVI-NFOA. It is concluded that using plant height information together with GreenSeeker NDVI can  improve the accuracy in N recommendations for rain-fed maize in Northeast China than only using NDVI.