Taking the Sichuan power grid as the object, this paper conducts the analysis of the influence of the UHVDC system blocking, caused by lightning strike, on the safe and stable operation of the sending power grid. The quasi-steady-state model of the UHVDC system is presented, the simulation model of Sichuan Power Grid including UHVDC systems under heavy load operation mode during the flood season in 2015 is established by using PSASP software. Based on the stability criterions of power system, the influences of the monopolar/bipolar latching of the UHVDC system caused by the lightning strike on the sending power grid are analyzed through simulations. This paper is of some reference significance for the stable operation of power grid with UHVDC system.