Abstract: Construction period of high core rock-fill dam filling relates to the construction progress and the project investment of a dam. While, traditional Monte Carlo simulation is based on constructing probabilistic model and sampling for the duration of network planning activity. This method cannot reflect the relation between duration and risk factors, which affects the objectivity and reliability of the simulation of the duration and the risk assessment. This paper applies improved set pair analysis method to filling construction schedule simulation and risk assessment of high core rock-fill dam, takes a full consideration of certainty and uncertainty of activity duration and relation between duration and risk factors, establishes network planning model of construction schedule Multiple connection number expressed by multiple connection number, and proposes Monte Carlo simulation process based on multiple connection number network planning. Taking a core rock-fill dam on Lancang River as an example, indicators like the distribution of duration, the probability of completion, the criticality of process, etc. are simulated, which provides evaluation standards for risks of rock-fill dam construction period. Compared with the traditional Monte Carlo simulation, this method can obtain simulation results that are more reliable and more consistent with engineering practice, which provides a scientific basis for risk assessment and risk management of high core rock-fill dam embankment construction period.