Abstract: The paper introduces a computational model of airspace conflict risk in the hierarchy of performance-based navigation (PBN) airspace operation and combines it with air traffic controller (ATC) workload to propose a method for safety assessment of PBN airspace operational planning. Capacity probability distribution is employed to depict airspace capacity in uncertain weather, errors of deviating from nominal PBN track are taken into consideration, and the stochastic process based on Gaussian distribution is used to depict random aircraft motion according to airspace PBN specification, so as to build an airspace conflict risk computational model in corresponding capacity scenario. Guangzhou No. 15 sector is chosen for simulation validation. The analysis results suggest that 60% of ATC workload is corresponding to sector traffic flow of 31 aircraft/h and airspace risk of 0.018 conflict/h, while 70% of ATC workload is corresponding to sector traffic flow of 35 aircraft/h and airspace risk of 0.03 conflict/h. As air traffic flow increases, both airspace conflict risk value and ATC workload will increase, resulting in reduction of airspace safety, though their increasing magnitudes differ with different capacity scenarios. The safety assessment method enables effective quantization of safety with regard to airspace operational planning strategy, and benefits the development of optimal operational scheme that balances risk with capacity demand.