The invention discloses a cast-in-situ 
straw / ash 
magnesium oxychloride 
cement wall and a construction method. The 
straw / ash 
magnesium oxychloride 
cement wall is obtained by 
processing straw, ash, light burned magnesia, 
magnesium chloride and the like and performing in-situ 
casting under the action of a modifier. The straw / ash magnesium oxychloride 
cement wall comprises the following raw materials in percentage by 
mass: 45 and 60 percent of magnesium 
oxide, 25 to 40 percent of solution of magnesium 
chloride, 2 to 20 percent of straw, 5 to 15 percent of ash and 0.5 to 2 percent of modifier. When the wall is cast in situ, the magnesium 
oxide, the solution of magnesium 
chloride, the straw, the ash and the modifier are mixed and stirred, and water is added into the mixture according to the water absorption of the straw to perform one-time forming through in-situ 
casting after the mixture is stirred uniformly. The wall is characterized in that the 
doping volume of the straw can be changed according to design requirements, and the straw can be used as inner and outer partition plates; the binding power is strong, so the 
adhesion process of the cast-in-situ wall materials and the conventional wall materials is avoided; due to the addition of the straw, the volume weight of products is reduced and the heat-insulating and heat-shielding performance of the products is improved; and a large amount of 
waste material ash, straw and the like is utilized to relieve the environmental burden effectively and reduce the cost, so the wall has great economic and 
social benefits.