Abstract: Highly regular and well-defined structured polyorganosilsesquioxane polymer with superior heat resistance, combustion resistance and flexibility, wherein same or different kinds of substituents are bonded alternately, and the preparation method thereof. The polyorganosilsesquioxane prepared according to the present invention has a small molecular weight distribution and a high molecular weight, and is soluble in organic solvents because a three-dimensional network structure is not formed during the preparative condensation polymerization. Polyalkylaromaticsilsesquioxane obtained from the preparing method of the present invention is a useful heat-resistant material. It can be used as a heat-resistant coating agent, a protective coating agent of optical fiber, a coating material for resistor, heat-resistant paint, an adhesive and a releasing agent for precise molding. Also, it can be used for the semiconductor protective layer, interlayer dielectrics for semiconductor integration (e.g.