Abstract: Two dimensional Minkowski space-time diagram is used to analyze twins effect. Clearly, natural Minkowski geometry line element length is proportional to the proper time of a particle;the space-time diagram comparing the world line length directly in different frames of reference is also used to analyze quantitatively the twins effect. In addition,the ＂three twin paradox＂ are qualitative and half quantitative analyzed.

Key words: Minkowski geometry, space-time diagram, twin paradox, proper time