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The three dimensional solidification simulation of the single crystal investment castings at withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min was performed with the finite element thermal analysis method. The calculated results were in accordance with the experimental ones. The results showed that with the increase of withdrawal rate the concave curvature of the liquidus isotherm was bigger and bigger and the temperature gradient of the castings decreased. No effects of withdrawal rate on the distribution of the temperature gradient of the starter and helical grain selector of the castings were observed at withdrawal rates of 2 mm/min, 4.5 mm/min and 7mm/min.The relatively high temperature gradient between 500°C/cm and 1000°C/cm in the starter and helical grain selector was obtained at three withdrawal rates. The study indicates the three dimensional solidification simulation by finite element method is a powerful tool for understanding solidification and predicting defects in single crystal investment castings.