The invention relates to a formula and a process for preparing a wide chlorinated polyethylene waterproof roll material through an extrusion molding method by an extruder. The process comprises the following steps of: uniformly mixing chlorinated polyethylene with various auxiliary agents through a certain material mixing method, and granulating through an internal mixer or a twin-screw extruder; and then, preparing a single-layer waterproof roll material or a double-layer waterproof roll material with self-adhesion surface by a coextrusion method of one or two extruders. The thickness of the roll material is adjustable from 1.2mm to 2.0mm, and the width thereof is 2.5 to 4.0m. The preparation process has the advantage of adopting a method of internal mixing extrusion granulation and extrusion sheet shaping by screw extruders to prepare the single-layer wide chlorinated polyethylene waterproof roll material or the double-layer coextruded wide chlorinated polyethylene waterproof roll material with one self-adhesion surface. The invention also has the advantages of high continuous degree, short production period, stable process, large-scale industrial production and controllable forming process; various properties of the manufactured roll material meet the requirements of waterproof, seepage-proof, moisture-proof engineering in rapid transit railway railroad bridge concrete decks or tunnels, and the like.