The GNSS time-frequency transfer receiver is widely used in time synchronization systems and nodes across various critical fields, where precise calibration of internal delay is essential for achieving high-accuracy time-frequency transfer. To address nanosecond-level time-frequency transfer requirements, experimental research is conducted on absolute and differential calibration methods for BeiDou time-frequency transfer receivers. First, the principles and differences of step-by-step, integrity absolute, and differential calibration methods are compared and analyzed. Based on GNSS anechoic chamber and common-clock-difference scenery, implementation plans are designed accordingly. Calibration comparison experiments are conducted for different types of BeiDou time-frequency transfer receivers at B1I, B1C, B2a, B3I, and L1 C/A to evaluate measurement uncertainty and analyze various calibration methods. The experimental results demonstrated that the measurement uncertainties of the step-by-step, integrity, and differential calibration methods are better than 0.71, 0.98 and 1.27 ns, respectively. The delay calibration values within each frequency point are consistent within the uncertainty ranges of the three calibration methods, verifying the effectiveness of the calibration comparison experiment and the superiority of the integrity absolute calibration method, forming a time-frequency signal calibration capability with sub-nanosecond uncertainty levels.