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In this paper, the wavefront perturbation method based on power detection of radio sources is used to measure the surface error of the Tianma radio telescope. By measuring the surface errors at different elevation angles, a surface compensation model to correct gravitational deformation is established. Observation results shows that the efficiency reduction caused by the gravitational deformation can be effectively compensated by loading this model on the active surface, especially at high and low elevations. A dual-beam calibration scheme is further used to remove atmospheric background fluctuations, which significantly improves data quality at lower elevations. The form and order of the perturbation modes and data processing are optimized to improve measurement accuracy. This paper presents the first attempt to apply the wavefront perturbation method to large radio telescopes and demonstrates its capacity and effectiveness in telescope runtime surface measurement and maintenance.