In dynamic control engineering, precise measurement of pendulum angle is crucial for achieving swing suppression. While binocular pendulum angle measurement methods rely on camera calibration results, changes in camera positions can introduce measurement deviations and pose challenges for efficient and stable measurements. To address these issues, this study proposes a monocular non-calibrated measurement method. The proposed method involves several key steps. First, continuous target image capture is combined with Kalman filtering and color space transformation to locate marker positions. Second, coordinate transformation based on cross-ratio is applied, comparing the current position with the initial position to calculate real-time pendulum angles through trigonometric transformations. Finally, a smoothing process using a combination of Gaussian and mean filtering is employed, and the results are validated against attitude sensor measurements. Experimental results demonstrate the effectiveness of the proposed method. Comparisons with binocular methods under variable-speed and constant-speed motion states yield the following findings: In variable-speed motion, the maximum pendulum angle is 1.871°, with a maximum angle error of 0.184°compared to the sensor. This represents an accuracy improvement of 0.018°over the binocular method. In constant-speed motion, the maximum pendulum angle is 3.075°, with a maximum angle error of 0.259°compared to the sensor, showing an accuracy improvement of 0.021 over the binocular method. Moreover, the computational efficiency is enhanced by 133.3%. When camera position deviations occur, the calibrated method produces maximum angle errors exceeding 0.5°compared to the sensor, while the non-calibrated method maintains errors below 0.3°. This non-calibrated approach effectively eliminates deviations, enabling accurate measurement of dynamic pendulum angles.