Optimizing irrigation schedules is essential for improving crop yield and crop water productivity (WPc) in arid and semi-arid regions. A field experiment was conducted to investigate the growth, yield and WPc responses of foxtail millet (Setaria italica L.) in response to three irrigation quotas (W1-3) with 150, 187.5, or 250 mm and with three different irrigation frequencies (T1-3) (seven, eight or nine irrigations) per season over each of two consecutive growing seasons in Ningxia, China. The results indicated that plant height, stem diameter, tiller number, panicle length and WPc increased and then decreased with increasing irrigation quota, while biomass increased steadily with increasing irrigation quota. The highest grain yields were recorded under W3T2 (8.40 t ha-1) in 2022 and W2T2 (8.37 t ha-1) in 2023, with no significant difference between yields of these two treatments. Yield was positively correlated with biomass and straw yield but negatively with panicle length and 1000-grain weight. The highest harvest index value occurred in W2T2 in both growing seasons. After a comprehensive evaluation based on grain yield, straw yield, 1000-grain weight, yield stability and WPc, the optimal combination of irrigation quota and irrigation frequency was the W2T2 treatment for millet using drip irrigation under plastic film in Northwest China.