Abstract: By theory analysis and test，some studies，which includs thin film material，sample preparation，elongation test and simulation test，are given to the error source and error control of mechanical property of space thin film material.And following measures can be used to decrease the error of mechanical property degradation test，which includes selecting samples with smooth rim；elongating in the direction of the normal direction of molecular principle chain，controlling the angle between elongation direction and length direction or thin film flat below 8°.When the angle above mentioned below 8°，the tensile strength will small than 1%.The ratio of shear force to tensile strength is tangential function of angle between elongation direction and length direction.