Abstract: The study, made by utilizing a large quantity of practical functional sample materials, with the aid of mathematical statistics and reliability theories, revealed the overall trouble rules of the functioning machine. The distribution function of the trouble and formularization expressions of the parameters of the function were presented. And the estimated value of the characteristic volume of the reliability and some very meaningful conclusions and recommendations were obtained. The study provides theoretical basis for deeper understanding of the status of caterpillar tractors in China and further improvement of reliability of the tractors. The study also helps us with mastering the status of functioning techniques, application of the machine and reasonably arranging operations.