Seismic vibrators are the primary sources for land seismic acquisition, featuring controllable bandwidth and energy, low environmental impact, safety, and high efficiency. With the widespread application of “2W&H” technology, wide-frequency seismic data, particularly low-frequency components, have attracted increasing attention. However, the ground force output of a vibrator is severely constrained at low frequencies, primarily due to limitations in its mechanical and hydraulic systems. Among these, hydraulic system limitations are often associated with oil flow, which is largely constrained by the pump’s maximum capacity; however, oil flow is not measured during vibrator sweeps. The system complexity prevents the installation of flow sensors on vibrators, making the performance of the vibrator oil flow unmonitored. Since the oil flow directly determines the quality of the vibrator ground force output, it is essential to understand the behavior of vibrator oil flow. In this study, a detailed analysis of the working mechanism of a seismic vibrator was conducted, as well as its low-frequency force-output limitations. Then, we proposed a method for estimating vibrator oil flow. Both theoretical analyses and field-testing data were used to validate the proposed estimation method. The estimated data demonstrated strong consistency with the direct flow measurement using flow sensors. Moreover, the results confirm the feasibility of the proposed estimation method. This method provides a real-time quality control indicator for the vibrator oil flow performance during vibrator sweeps, thereby enabling complete monitoring of the vibrator performance quality at low frequencies. In addition, this method holds promising potential for broad application in land vibroseis exploration.