Abstract: The propagation loss of waveguide is a key indicator to evaluate the performance of an integrated optical platform. The commonly used cut-back method to measure the propagation requires the introduction of the Spiral test structure. In order to remove the effect of bending loss, the bending radius is usually designed to be large enough, taking up a lot of foot print. In this paper, we suggested a method to measure the propagation loss and bending loss of waveguide simultaneously with cut-back structure. The bending loss can be exponentially fitted with the bending radius according to simulation, which can be further simplified as linear fitting between the natural logarithm of the bending loss and the bending radius. A genetic algorithm was used to fit the insertion loss curve of the cutback structure and calculate the propagation loss and bending loss. With this method, we measured a cut-back structure of lithium niobate waveguide and got the propagation loss of 0.558dB/cm and bending