Abstract: In order to study the value problem of concrete strength in the identification of existing structures, through the analysis of the the concrete strength distribution, the normality test method is used to identify the reasons for the difficulty of obtaining the concrete strength. The concept of the target standard deviation is proposed for the quick analysis of the outliers and supplementing sample sizes. The results indicate that the three main reasons for the difficulty of obtaining the concrete strength are samples not from the overall sample,the concentrated sampling and the large standard deviation of the overall sample. The concrete strength values can be confirmed cautiously by the consideration of the safety of the structure, the feasibility and economy of subsequent reinforcement.The methods that can be used include data normality, sampling distribution, outlier removal, supplementary sampling, and value justification.