The work is a truly scientific theory on relativity in physics, since it contains no any hypothesis and all the results presented were soundly deduced by using deductive reasoning methods; therefore, if the principles revealed in this book could be wrong, it would be no correct theory of relativity in physics presently. The work consists of relativity on inertial motion, rectilinear acceleration, circular motion and relativistic dynamics, which forms a complete knowledge system on relativity; the author had tried to make all the derivation processes in this book as intuitive as possible, and also tried to avoid very complicated mathematical handlings; for the one who has B.S. level should be able to well understand this work. Many principles revealed in this book are really surprising and amazing but truly scientific; hope that you will enjoy reading this book.