the pendulum length very accurately. Under the better measurement conditions，the measurement accuracy

could generally reach the order of millimeter，and the relative error of the measured gravity acceleration is generally

about 1%. In order to solve this problem，in this paper the measuring precision was improved to 0.02mm by using

avernier caliper connected with a cycloid to accurately measure the change of pendulum length instead of directly

measuring the pendulum length. At the same time，the swing period of the pendulum ball is measured by a photoelectric

gate，and the different cycloid material and diameter are compared and analyzed.The measurement error of

acceleration is controlled within 0.1%.