In response to the sensitivity of greenhouse small agricultural machinery to ground flatness, small ground undulations can cause the equipment to pitch. Based on the greenhouse electric tractor developed by the research group, the method based on time series analysis was introduced into angle prediction and feedforward PID control (APF-PID) to solve the problems of poor responsiveness, unstable tillage depth, and sudden power changes caused by equipment pitch in greenhouse rotary tillage operations. Firstly, a power model for greenhouse electric tractor rotary tillage operation was established, and a conversion matrix between pitch angle and tillage depth was established to obtain the conversion value of the actual tillage depth of the rotary tillage system. Secondly, time series analysis was used to predict the pitch angle of the aircraft body and serve as disturbance input for the rotary tillage system. Then, combining the conversion value of tillage depth and the predicted disturbance, the APF-PID controller was used to adjust the lifting mechanism of the rotary tillage system, and the rotary tiller was maintained at the target tillage depth. Finally, actual vehicle experiments were conducted on two types of plots in a greenhouse, one without rotary tillage and the other with rotary tillage. The results showed that the correlation coefficient of the pitch angle time series prediction model can reach 0.9832, the control performance of APF-PID control was superior to that of PID control. In the test road surface with a target tillage depth of 6cm, the average tillage depth of APF-PID on two test plots was 6.47cm and 6.44cm, with root mean square errors of 0.80cm and 0.72cm, absolute average errors of 0.67cm and 0.58cm, and tillage depth stability coefficients of 89.95% and 91.30%, respectively. The total energy consumption was reduced by 4.18% and 19.13% compared with that of PID control, which effectively achieved the stability control of greenhouse electric tractor rotary tillage and met the requirements of greenhouse operations.