Water jet-guided laser is a new type of processing technology. With the continuous emergence of high hardness, high strength materials and the demand for high-efficiency processing, water jet coupled high power laser has become an inevitable trend in the development of the water-guided laser, and high-power laser energy and water jet coupling transmission and processing process will bring a series of problems such as transmission loss, these will become one of the key issues limiting the development of this technology. Therefore, studying the transmission loss of high-power laser energy guided by water jets is necessary. In this paper, we address this problem by numerically solving Maxwell's set of equations using the finite element (FEM) method and performing wave optical simulations of high-power laser transmission in a water jet to obtain the electric field distribution of the laser beam in the water jet, and explore the relationship between laser wavelength, laser spot diameter, water jet diameter and length, and laser energy loss. Finally, laser energy transfer efficiency measurement experiments were conducted to verify the model's validity by comparing it with simulation data. The study's results will provide some implications for regulating the transmission efficiency of high-power lasers in water jets.