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To improve the spray fire extinguishing performance of magnesium-hydroxide gel dry-water powder, this paper studied the preparation speed, material mass ratio, fluidity, bulk density, pressure resistance, and fire extinguishing performances of modified dry-water powders. A pure-water dry-water powder was modified by applying an effective extinguishing component, magnesium hydroxide, and a coagulant, Gellan gum. The preparation process parameters of the pure-water dry-water powder system were optimized. The results showed that the optimal process parameters for the preparation of dry-water powder were a rotation speed of 4000 rpm, an SiO 2 :H 2 O ratio of 9:100, and a stirring time of 3 min. The resting angle of magnesium-hydroxide gel dry-water powder was below 28°, with good fluidity. The bulk density of the dry-water powder was lower than that of the BC-class dry powder extinguishing agent, and the bulk density of the magnesium-hydroxide gel dry-water powder was 0.467 g·mL−1. With the increase in pressure, the damage rate of the dry-water powder increased. The addition of magnesium hydroxide and Gellan gum significantly improved the pressure resistance of the dry-water powder. At a pressure of 1.4 MPa, the magnesium-hydroxide gel dry-water powder was only 11% damaged. The performance of the magnesium-hydroxide gel dry-water powder was improved by 37.21% compared with the average cooling rate of the BC-class dry powder extinguishing agent used as a control fire extinguishing group. The dry-water powders produced by modifying the dry-water powders with magnesium hydroxide and Gellan gum could withstand higher driving pressures, and they had improved powder diffusion, reduced powder charge volume, and increased fire extinguishing properties compared with those of the other dry-water powders. [Display omitted] • Modifying dry-water powder allows it to obtain new and improved properties. • A new gel dry-water powder was produced using magnesium hydroxide and Gellan gum. • Spraying and extinguishing tests were conducted on the new dry-water powder. • The new gel dry-water powder was 37.21% more efficient than BC-class dry powder. [ABSTRACT FROM AUTHOR]