The invention relates to a preparation method of silicon sheet varnish, particularly a preparation method of water-soluble low-contact-angle half-inorganic silicon sheet varnish. The invention aims to solve the problems of low dispersity and large contact angle of paint liquid powder, and the problem of low volume resistance of the paint film in the existing silicon sheet varnish preparation method. The method comprises the following steps: adding dibasic acid, dibasic alcohol and tribasic alcohol into a reaction kettle; after heating, adding a catalyst, heating and keeping the temperature; cooling the reaction system, heating and keeping the temperature; heating the reaction system three times, cooling, adding polybasic acid, and keeping the temperature; cooling to room temperature, and adding long-chain curing agent, neutralizer and cosolvent to obtain an organic phase; adding the organic phase, short-chain curing agent, inorganic phase and assistant into an ultrasonic reaction kettle; and carrying out ultrasonic dispersion, and discharging to obtain the half-inorganic silicon sheet varnish. The invention enhances the dispersity of the inorganic phase, and reduces the contact angle of the paint liquid, so that the applied paint film is smoother. The invention is applied to preparation of silicon sheet varnish.