Interferometric synthetic aperture radar (InSAR) is an effective digital elevation model (DEM) generation tool. High-precision InSAR DEM requires an accurate baseline. The baseline accuracy can reach 2 mm in the TanDEM-X mission. However, compared with the X-band, the L-band has the characteristics of long wavelength, strong penetrability, and low backscattering coefficient, which leads to the elevation error caused by the penetration depth and the signal-to-noise ratio (SNR) decorrelation cannot be ignored. Therefore, this paper proposes a baseline calibration method with compensation for additional height error caused by penetration depth and SNR decorrelation. Aiming at the baseline calibration of L-band InSAR TwinSAR-L (LT-1), this paper calculates the calibration accuracy of proposed calibration method by using Advanced Land Observing Satellite-2 (ALOS-2) data when taking desert as the calibration field. The results show that the baseline error before additional elevation error compensation is $2.6 \text{mm} (1\delta)$, and reduces to $0.85 \text{mm}(1\delta)$ after compensation. Therefore, the baseline calibration method in this paper can effectively realize the baseline calibration of LT-1.