Abstract: This work researches the relationship between desired speed ratio of continuously variable transmission (CVT) and desired engine speed and analyzes the characteristics of speed ratio of geometric type hydro-mechanical transmission (HMT) and its shift conditions. The method of simulating engine characteristic using drive unit of test bench was adopted. The tests of governing engine speed by applying speed ratio follow-up control system were implemented. By analyzing the test results, the engine speed governing rule based on the speed ratio follow-up control system of CVT was given. It could be stated as follows. When the rate of desired speed ratio gets larger, the follow-up control error of engine speed will be larger; on the contrary, the error will become smaller. When the actual speed ratio is larger than the desired speed ratio, the engine speed will be smaller; on the contrary, the engine speed will become larger than actual speed.