Four Signs is one of the most famous novellas in The Adventures of Sherlock Holmes, the masterpiece of Conan Doyle. Its long-term and far-reaching influence has won the love of readers at all levels. According to the appearance and details in life, the work uses imagination and experience, and deduces terrible and amazing inferences with meticulous and impeccable logical reasoning. Author Conan Doyle has brought the great energy of human observation and logical reasoning into full play. The content of the work involves the social reality of Britain at that time, and the logical reasoning is fascinating.