Research conclusions : If the allowable stress method is used , it is not necessary to differentiate the kinds and condition of service of the members. According to allowable strength, the different load types have the same safety coefficient K to make the structure design safer and more conservative. Probability limit state method based on probability statistics has objectivity and reasonableness, superior to allowable stress method with subjectivity and experience. However for the particularity of railway train load, the reliability of probability limit state method is not mature. Thereby at present the allowable stress method shall be adopted in the design of pile-slab structure. It is hoped that in the near future probability limit state method will take the place of allowable stress method.