The invention relates to a preparation process for water-pressure-resistant flame-retardant polyester canvas. The preparation process comprises the following steps: (1) preparation of canvas: a, proportioning of components of yarns; b, spinning: uniform blending the components, and blending conductive fibers with other fibers by using a Siro-spinning process to ensure each yarn contains the conductive fibers, wherein ply yarns are used, and moderate twisting is performed; c, weaving: carrying out weaving by using an air-jet loom or a rapier loom according to the process flow consisting of singeing, desizing, boiling-off, bleaching, mercerizing, dyeing, flame retardation treatment, ammonia fumigation, oxidation, washing, drying, baking and preshrinking; (2) preparation of an impregnating solution; and (3) dip-padding of the canvas in the impregnating solution, and drying at 150 DEG C for 2 to 3 h. The polyester canvas prepared by using the preparation process improves the bonding strength of the canvas and guarantees the flame retardation performance of the canvas without any influence on the other indexes of the impregnated canvas, and is applicable to working clothes.