A parallel measurement approach is presented to analyze multiple linear polarization (LP) modes using the spatial light modulator (SLM). The hologram loading onto SLM is generated by conjugate symmetric extension Fourier computer-generated holography. The mode array containing different LP modes is encoded into the hologram, which records the array amplitude and phase information. Demodulated by the SLM, the modal content and their relative powers of tested light are obtained by measuring the intensity and position of the demodulated light spot in the diffracted field. The experimental system is established and LP modes of single and few-mode step-index fibers are measured. Our method has some advantages, including simple optical setup and applicability of the higher-order modes detection. It is promising for the mode analysis of high-power fiber lasers and optical communication.