Biodiesel was prepared from castor oil and methanol by transesterification with magnesium aluminum hydrotalcite as catalyst. It was mainly discussed that the ratio of alcohol and oil, temperature, catalyst dosage and reaction time influenced the yield of biodiesel from castor oil through single factor experiment and response surface experiment,and the composition contents of the biodiesel were determined by gas chromatography, and the density and viscosity index of the diesel fuel were compare with 0 # diesel oil. The results show when the ratio of alcohol and oil of 8∶1, the temperature is 65 ℃, catalyst dosage of castor oil is 1.00%， reaction time is 3 h and stirring intensity is 700 r / min, the yield of biodiesel  can reach 87.3%.