In view of magnetoresistance effect of perovskite manganite in low magnetic field，manganite polycrystalline samples La0. 7 － xYxSr0. 3MnO3 ( x = 0，0. 1，0. 2) were prepared by solid-state reaction technique. Xray diffraction spectrums of the two samples ( x = 0，0. 2 ) and resistance-temperature ( R-T ) curves and magnetoresistance-temperature ( MR-T) curves of the three samples ( x = 0，0. 1，0. 2) in zero magnetic field and 0. 25 T magnetic field were measured. Influence of different substitution of Y for La on low field magnetoresistance effect of the samples was analyzed. Experimental results showed that the crystal structure of the sample La0. 7 Sr0. 3 MnO3 was distorted from cubic structure to tetragonal structure and that of the sample La0. 5Y0. 2 Sr0. 3MnO3 was cubic structure. The lattice constants decreased with the increase of Y doping in La site from x = 0 to x = 0. 2. The R-T curves of the three samples did not appear the metal-insulator transition peak in the experimental temperaturerange，showing the metal resistance temperature characteristics. At the same temperature，the resistance of the three samples in magnetic field was smaller than that in zero magnetic field， showing the negative magnetoresistance. The MR-T curves of the three samples showed no peak temperature TP and the magnetoresistance increased with decreasing temperature. The three samples showed obvious low field magnetoresistance effect in the experimental temperature range in 0. 25 T magnetic field. This paper provided an important reference for application research of perovskite manganite in the field of magnetoelectronics.