The invention discloses an error analysis method for measuring the bridge deflection by a tilt angle sensor. According to the principle of deflection measurement by a tilt angle sensor, an easy-to-useconvenient-to-use deflection calculation model being a segmented superposition model is selected; and an error of the measurement method is studied based on the model. According to the deflection calculation model, two sources, including a segmentation error and inclination accuracy of a tilt angle sensor, of a measurement error are determined. In order to calculate influences on the final deflection measurement error by two error sources comprehensively, sampling distribution analysis is carried out on a deflection measurement value in a simply supported beam after consideration of the tiltangle measurement accuracy under different segment numbers according to a Monte Carlo method; and thus a deflection measurement value distribution mean value, a standard difference, a 95% probabilityconfidence interval and the like are obtained and the error is determined. And according to error results obtained by using different angle measurement accuracy sensors under different segmentation conditions, applicable sensor accuracy and segmentation methods under different working conditions are provided.