The invention belongs to the technical field of polysiloxane synthesis, and particularly relates to hydrogen-containing silicone oil and a preparation method thereof. A molecular formula of the hydrogen-containing silicone oil is as shown in the specification, wherein n is 200-500; and R is CH3 or CH2CH3. The preparation method comprises the following steps: (1) adding a linear body to a reaction kettle, stirring, warming to 130-140 DEG C, and adding potassium hydroxide; (2) carrying out vacuum supply, and detecting the viscosity online, when the appointed viscosity is achieved, restoring into atmospheric pressure and adding phosphoric acid or silicon-based phosphate for neutralization; (3) cooling, adding methyldialkoxysilane and a catalyst, and carrying out stirred reaction; and (4) warming, carrying out vacuum supply and removing low molecules to obtain the hydrogen-containing silicone oil. The hydrogen-containing silicone oil provided by the invention can be used as an addition-type silicone rubber chain extender or is applied to the aspects of synthetic fabric finishing agents and the like; the linear body and the methyldialkoxysilane which is low in cost and easy to prepare are adopted as raw materials, so that the raw material cost is reduced.