With the increase in output power of high power semiconductor lasers(HPSLs), thermal management is one of the critical bottlenecks affecting the optical-electrical performance and reliability of HPSLs. Thermal characteristics of a kW-level conduction cooled semiconductor laser array were analyzed based on numerical simulations and experiments. Firstly, transient thermal behavior was studied using finite element method (FEM). There is significant "thermal crosstalk" behavior among the semiconductor laser bars with pulse width greater than 250 μs. It shows thermal resistances along horizontal and vertical directions are 64.7% and 35.3%, respectively, indicating that heat mainly dissipates along horizontal direction. 74.9% of thermal resistance along horizontal direction and 66.5% of thermal resistance along vertical direction origin from CuW layer, which shows that CuW is the most significant factor affecting the efficiency of thermal dissipation. Based on accumulated average temperature method, the simulated temperature differences are 2.13, 1.47, 0.75 ℃ at the repetition frequencies of 20, 30 and 40 Hz compared with that at the frequency of 50 Hz. Average junction temperature rises at different repetition frequency have been measured using spectral method, and the temperature differences at the repetition frequencies of 20, 30 and 40 Hz are 2.33, 1.56, 0.78 ℃, respectively. The average error is less than 6.85% between experiment results and numerical simulation. It shows that the simulated transient thermal resistance is coincident with the experimental result.