Machine-made rock sand (M-sand) as a replacement of river sand has been promoted as an environmental-friendly substitute in concrete. It is acknowledged that the stone powder in M-sand has an adverse influence on performance of concrete. This study investigated the influence of stone powder contents from 3% to 15% on mechanical properties of M-sand C80 concrete. As per experimental results, adopting the arithmetic mean method from experimental results hardly determined the optimum stone powder content for various mechanical properties of high-strength concrete due to high variation. A statistical analysis method was thus developed to verify the influence of stone powder content on mechanical properties of concrete. A new random variable was first constructed by considering the standard value, followed by the standard normal distribution. Meanwhile, the type I error in statistical hypothesis testing was further adopted. It was found that this developed statistical method can further verify experimental results through a standard value method, which can be used for practical engineering applications in accordance with specifications and provide a way to optimize the stone powder content in high strength concrete for experiment-oriented researches.