The invention discloses a continuous magnesium hydroxide washing and separating method and system. The method includes: diluting to-be-treated magnesium hydroxide slurry by a washing solvent in set temperature to obtain first diluent, and inputting into a separating or filtering component to obtain a liquid phase and solid slurry containing magnesium hydroxide through separation; using the washingsolvent for diluting the solid slurry obtained in separation to obtain second diluent, and inputting into the separating or filtering component to obtain the liquid phase and solid slurry through separation, wherein a volume ratio of the washing solvent to to-be-treated magnesium hydroxide slurry or solid slurry obtained in separation is 0-50:1; repeating the above operation for more than one time, measuring a pH value or concentration of impurity ions in the liquid phase obtained in each-time separation until the pH value or concentration of the impurity ions is decreased to a target value.Solid slurry feeding, discharging, system temperature control and the like can be controlled through a DSC control system to realize continuous magnesium hydroxide washing and solid-liquid separation,and industrial automatic separation and washing can be realized easily.