The invention discloses a transmission type Mueller matrix spectrum ellipsometer and a measuring method thereof. The transmission type Mueller matrix spectrum ellipsometer measuring method comprises the following steps: projecting modulation rays produced by a partial arm on the surface of a to-be-tested sample, a check partial arm demodulates and receives the rays reflected (or transmitted) by the to-be-tested sample, by proceeding
harmonic wave analysis to a tested spectrum, computing and acquiring the full Mueller matrix information of the to-be-tested sample, further through arithmetic of
nonlinear regression, liberty matching, and the like, and fitting and extracting information of an optical constant, characteristic, morphology, size and the like of the to-be-tested sample. An ellipsometer comprises the partial arm (comprises
light source, a lens group, a
polarizer, and a compensator driven by a
servo motor),the to-be-tested sample and the check partial arm (comprises the compensator driven by a
servo motor, an analyzer the lens group and a
spectrograph. The transmission type Mueller matrix spectrum ellipsometer and the measuring method thereof can achieve all kinds of materials and components with information phoelectron functions, and online measurement of all kinds of nano-structures in nano-fabrication, so that transmission type Mueller matrix spectrum ellipsometer and the measuring method thereof have the advantages of being capable of possessing non-destructive property, fast, and low in cost.