Abstract: The earth s rotation brings a lot of non - inertial effects. It is a significant aspect of physics 　　experimental research to measure rotational angular velocity of the earth quantitatively with these effects. Among 　　them，Bravais pendulum can no longer present the effect of the earth qualitatively，but also provides a method to 　　measure its rotation period precisely. We explore the experiment deeply which is conducted to measure the earth s 　　angular velocity by the difference of periods clockwise and counterclockwise. We also analyze the key factors that 　　influence the accuracy of measurement and discusses the ways to control the experimental errors. Finally，we get the 　　result with 2. 25% deviation compared to the standard value. Since the difference caused by the earth s rotation 　　between periods clockwise and counterclockwise is quite tiny and there are abundant factors influencing the 　　measurement of periods，to control the major errors becomes vital to the success of this experiment. We introduce 　　the ways to control the condition and some analysis of some important deviation sources. It can ben taken as a 　　reference for measuring rotational angular velocity of the earth under plain condition.

Key words: Bravais pendulum, conical pendulum, measure, earth s rotation, angular velocity