For the diameter of 150mm elliptical flat mirror that used in the space, Selected the zerodur material and a lightweight design is conducted in the way of selected back-open-architecture with symmetrical axisymmetric arrangement, and in order to evaluate the effect of thermal stress from -10 degrees C to 45 degrees C on the mirror, a reflection mirror is designed based on the multipoint flexible support. The mirror component's mechanic and thermodynamic characteristics is analyzed with the simulation software, the support structure parameters are optimized, that can be used to evaluate the effect of gravity, assembly stress, and thermal stress load on mirror, while ensuring the component's stiffness and strength. According to the design condition developed a product and carried out mechanic and thermodynamic environment, the product could meet the shape accuracy PV lambda/3, RMS lambda/30 in the condition of thermodynamic environment, and the shape accuracy PV lambda/5, RMS lambda/40 in the condition of ground gravity and assembly stress (lambda= 632.8nm), while the product can withstand with the mechanical oscillation environment sinusoidal oscillation 10g, RMS random oscillatin acceleration 14.4g.