The invention discloses a mask assembly assembling method. The mask assembly assembling method comprises steps of external force application, tension application, alignment installation and external force release. The mask assembly assembling method is characterized in that through one or more tension application steps, alignment installation steps and external force release steps, one or more mask units are installed to a mask frame; and after all the mask units are installed, all external forces are released so that a mask assembly is obtained. Through the mask assembly assembling method, the shape of the mask frame provided with all the mask units is basically the same as that of the mask frame without the mask units, in other words, the shape of the mask frame is basically unchanged and thus a mask assembly precision is improved so that a precision and quality of the product are improved.