The point load tests of an andesite have been carried out, and the results of probability analysis have shown that point load strength indexes submit to normal distribution. The quantitative relationship between the uniaxial compressive strength and point load strength index has determined by uniaxial compression test and the confidence interval has been discussed also. The analysis results demonstrates that the on - site point load test of rock can meet the need of generic engineering design ff test samples of rock are chosen according to normality conditions.