A measurement method of Müller matrix is proposed based on the trajectories on the Poincare sphere. A matrix obtained by the polar decomposition is related to its trajectories on the Poincare sphere. Therefore, the birefringence and dichroism matrices of a nondepolarizing unit are directly obtained via the position relationship of the input and output light polarization states on the Poincare sphere. The results show that, based on the proposed method, only one rotatable polarizer is required in the polarization control system. With the measurement of two polarization states determined before and after tests, not only the birefringence and dichroism matrices can be directly obtained, but also the state of the fiber to detect does not need change during the measuring process.