The invention belongs to the field of polysiloxane synthesis technologies, and particularly relates to a preparation method of low-viscosity 107 silicone rubber. According to the method, dimethyl dichlorosilane is hydrolyzed, an annulus body and a linear body are separated, carbonate is added into the separated-out linear body, temperature is raised to conduct reaction under negative pressure, the negative pressure is restored to normal pressure after viscosity reaches 300-1500 Pa.s, and low-molecular substances are drawn out through filtration to obtain the product. The viscosity of the prepared low-viscosity 107 silicone rubber is 300-1500 Pa.s and can be easily and accurately controlled, and reaction is mild. No low-molecular cyclosiloxane is generated in reaction, and the yield is greatly increased and reaches above 96%. A catalyst can be removed just through filtration and can also be recycled.