The invention discloses a preparation method of a high-tenacity low-water absorbability carbon oxygen crosslinked polyvinyl acetal insulating material, and belongs to the field of high-polymer materials. The preparation method comprises the following steps: taking polyvinyl alcohol as a raw material, dissolving polyvinyl alcohol with deionized water, cooling, carrying out a reaction between polyvinyl alcohol and a part of acetaldehyde at a low temperature under the catalysis of an inorganic acid, adding the rest acetaldehyde when the temperature is lowered to a proper temperature to ensure acetalization between the rest acetaldehyde and polyvinyl alcohol, heating to 40-60 DEG C at a temperature rising rate of 4-16 DEG C/h to ensure acetalization, separating polyvinyl acetal and an acid liquid via a centrifuger after acetalization is finished, washing the obtained polyvinyl acetal in a vacuum suction filtration washing machine with deionized water and dilute alkali, and carrying out centrifugal drying and pneumatic drying to obtain the product polyvinyl acetal. The carbon-oxygen-crosslinked polyvinyl acetal insulating material is excellent in strength, tenacity, weatherability, water resistance, and decay resistance, low in water absorbability, beneficial in tear resistance, high in service performance, wide in application range, and suitable for industrialized production.