The upwelling growth and evolution of spherical bubble clusters appearing at one-quarter wavelength from the water surface in ultrasonic cavitation fields at frequencies of 28 kHz and 40 kHz are studied by high-speed photography. Due to the interactions of bubbles, the stable bubble aggregation occurs throughout the rise of the bubble cluster, whose vertical pressures difference leads to a more significant spreading in the upper part of the cluster in the standing-wave field. At 28kHz, the rising speed is about 0.6m/s, controlled by the primary acoustic field. After a violent collapse of the bubble clusters, the aggregating structure began to hover near the water surface. The size and stability of the structures are affected by the frequency and pressure of the primary acoustic field. If two clusters are close to each other, the clusters deviate from the spherical shape, even trailing off, and eventually merge into a single bubble cluster. By considering the influence of water-air boundary, based on the mirror principle, a spherical bubble cluster model is developed to explore the structure stability of the clusters, and the modified dynamics equations are obtained. The effects of driving acoustic pressure amplitude, bubble number density, depth from the water surface, and bubble equilibrium radius on the optimal stabilization radius of the spherical bubble cluster are numerically analyzed using the equivalent potential at 28 kHz and 40 kHz. The results show that the optimum stabilizing radius of spherical bubble cluster is in the range of 1~2 mm, and it tends to decrease slightly with the increase of the the driving acoustic pressure and bubble number density. It is worthy to note that the nonlinearity is enhanced by increasing acoustic pressure, which may promote the stability of the structures of the cluster. The smaller the unstable equilibrium radius, the easier it is to grow, and the stable size at 40 kHz is slightly smaller than that at 28 kHz. Generally, spherical clusters first appear in high-pressure zone, and then translate toward the low-pressure zone. If the acoustic pressure falls below a certain critical value, bubble clusters disappear. The theoretical analysis is in good agreement with the experimental observations. The analysis of the growth and structural stability properties of spherical bubble clusters contributes to the understanding of the behavioral modulation of bubbles.