The invention discloses a monofunctional trimethyl silane (M) quadrafunctional silicon tetrachloride (Q) organic silicon resin and a preparation method thereof. The MQ organic silicon resin is prepared by the reaction of the following components in percentage by weight: 15.0 to 30.0 percent of sodium silicate, 10.0 to 25.0 percent of hexamethyldisiloxane, 1.00 to 10.0 percent of dimethylchlorosilane, 0.20 to 3.00 percent of concentrated hydrochloric acid, 30.0 to 50.0 percent of mixed alcohol and 10.0 to 25.0 percent of deionized water. Compared with the prior art, when the preparation methoddisclosed by the invention is used for producing the MQ organic silicon resin, a complex 'extraction-washing-liquid separation' treatment process is not used, and industrial production is simpler andmore reliable.