Abstract: With the decline of system inertia in modern power systems, frequency issues following disturbances have become increasingly severe, and the deployment of grid-forming energy storage has gradually emerged as an important means for primary frequency regulation. However, improper parameter settings of grid-forming energy storage may aggravate transient stability risks, and existing studies generally neglect the state of charge (SOC) constraints of the storage system itself. To address this issue, this paper proposes a primary frequency regulation method for grid-forming energy storage considering SOC constraints and active frequency modulation coefficients.First, a detailed mathematical model is established to describe the coordinated participation of grid-forming energy storage and synchronous generators in primary frequency regulation, and the system frequency response transfer function is derived. Second, based on trajectory sensitivity analysis, the key dominant parameters affecting transient frequency stability are identified, and a parameter optimization model is constructed with the objective of minimizing the maximum system frequency deviation. The model incorporates constraints on the SOC safe operating range, output limits, and the rate of change of frequency (RoCoF), and is solved using the sequential quadratic programming (SQP) algorithm. Finally, simulation results demonstrate that, under SOC and RoCoF constraints, the proposed method reduces the maximum frequency deviation by 43.3% and significantly raises the frequency nadir, thereby effectively enhancing the transient frequency stability of the power system.