Abstract: The existing electromagnetic transient simulation algorithm can accurately reflect the operation characteristics of line commutated converter based high voltage direct current（LCC-HVDC） transmission systems, but the amount of computation is large. In order to improve the simulation efficiency of LCC-HVDC transmission systems, the existing electromagnetic transient simulation model of LCC-HVDC transmission systems is simplified, and the integrated electromagnetic transient simulation model and solution algorithm of LCC-HVDC transmission systems are proposed. The integrated model includes the converter transformers and the converter valves. The converter transformer adopts the simplified model and the converter valve adopts the ideal switch model, which can simplify the electrical network structure of the converter. In this algorithm, the electrical network topology of converters is divided into the main network and the sub-network. First, the main network is solved, and then the subnetwork is solved according to the obtained results. Finally, the current and voltage of each converter valve in the current simulation step size are updated. The integrated electromagnetic transient simulation model and algorithm are programmed in the PSModel simulation software, and its efficiency and accuracy are verified by comparing with the PSCAD/EMTDC simulation results.