To determine the influence of biochar addition on maize yield and water-fertilizer use efficiency under limits of soil suction to trigger irrigation for mulched drip irrigation in saline-alkali areas, proposing the optimal irrigation schedule and biochar application rate, a field experiment from 2015 to 2016 was carried out in the maize growth stage of the salinized farmland in the Hetao Irrigation District. Three limits of soil suction to trigger irrigation [-15 (W15), -25 (W25), -35 (W35) kPa, and the irrigation quota was 22.5 mm] and three application rates of biochar were designed. Biochar was just only applied in the first year. Soil physochemical properties in top 15 cm layer, crop growth characteristics, water and nitrogen use efficiency and economic benefits of maize in the whole growth period were measured and analyzed. The results showed that the application of biochar at different irrigation water limits increased the soil water content, organic matter, and available nitrogen content in the whole growth period of maize. For same irrigation level, the higher the amount of biochar, the greater the improvements of these measurements. Application of biochar significantly increased the dry matter accumulation and grain yield of maize plants; the irrigation water use efficiency and the partial fertilizer productivity of nitrogen were also significantly improved. Compared with the control without biochar, under the conditions of W15, W25 and W35, B15 increased corn yield by 12.8%, 10.3% and 14.2%, irrigation water use efficiency increased by 14.2%, 10.4% and 12.9%, and nitrogen fertilizer partial productivity increased of 12.8%, 10.4% and 14.0%. For same irrigation treatment, the effect of B15 in saving water, enhancing yield was generally better than that of B30. It is suggested that the limit of soil suction to trigger irrigation is -35 kPa (22.5 mm for each irrigation) under mulched drip irrigation during the growth period of maize in salinized farmland, and the application rate of biochar is 15 t/hm².