Abstract: In the long-term development, DC transmission projects may form a relatively fixed control strategy. Ameliorating the strategy is of great significance to improving the stability of AC/DC hybrid power grid. In recent years, the electromechanical electromagnetic hybrid simulation technology has been used for stability analysis. Under some serious faults on the AC side of large power grid, several ultra-high voltage DC (UHVDC) projects based on line commutated converter (LCC-UHVDC) are found to have the risk of continuous large-scale power oscillation by using the simulation technology, indicating that the existing control strategy may be further improved. This paper introduces the similar power oscillation phenomenon in several UHVDC projects, and takes an UHVDC project as example to deeply analyze the mechanism of power oscillation induced by some modules of LCC controllers, such as commutation margin area calculation module (AMINCALC), maximum arc angle limited direct output module (GAMMA0) and voltage dependent current order limiter (VDCOL). The possible control measures to suppress this kind of oscillation and the practical control optimization scheme are studied. The effectiveness of the scheme is proved by the simulation of the actual power grid.