A capacitive micromachined ultrasonic transducers (CMUTs) array with dual-mixed radii is designed to improve bandwidth and realize multi-modes operating for immersed ultrasonic applications. The two-size (TS) CMUT array is composed of two sub-arrays with different membrane radii, but the same cell arrangement. The two sub-arrays are separately connected to external power sources to achieve separate control of each array. An electromechanical-acoustic coupling simulation model of the TS-CMUTs array is established by finite element method to investigate their impedance and conductance properties under different DC voltages in the frequency domain. The results indicate that the designed CMUTs can operate with a significant improved frequency bandwidth ranging from 9.75 MHz to 13.35 MHz by adjusting the DC bias voltage. Compared with traditional CMUTs arrays, the proposed CMUTs array can contribute to an increase of up to 270% in the bandwidth.