A new small rotation angle measurement method is proposed to solve rotation angle measurement problems during structural stiffness tests. The tangential displacement of object is measured by laser displacement sensor

and is converted to rotation angle values through geometry relationship. A mathematical model for error is established to analyze each error factors which have effects on measurement results. Within the measurement range of ± 1°

measurement results affected by error factors are respectively studied

which drew the conclusion that the offset Δl between light spot and engraved lines mark has greater influence on errors. The torsional stiffness of a profiled member is tested as an application of this method when Δlis equal to ± 1 mm

measurement errors are about 2 %

which verify validity and accuracy of this method.