Broadband acoustic focusing effect based on a thermoacoustic phased array is studied. In this work, according to the relationship between the sound velocity and the temperature, a new type of a thermoacoustic phase control unit is designed by using air with different temperatures surrounded by rigid insulated boundaries and thermal insulation films. The acoustic wave velocity could be adjusted by changing the temperature of air in the unit, and the transmitted and reflected acoustic phase delays can cover the whole 2 interval. On the basis of this thermoacoustic phased array, we design four different types of acoustic focusing lenses. By using eight or two kinds of such units, we realize the transmitted and reflected acoustic focusing effect, respectively. The results show that the thermoacoustic phased array lens has a good focusing performance in a frequency range of 4.0-15.0 kHz. In addition, the center intensity of the focal spot is much greater in the focusing lens with eight phase units, and the design method is simpler and more robust in the focusing lens with two phase units. Compared with other types of focusing lenses, the proposed focusing lens based on the thermoacoustic phased array has the advantages of broad bandwidth, high focusing performance and simple designed method. The results provide a theoretical basis and experimental reference for designing the broadband thermoacoustic phased array devices and new types of acoustic focusing lenses.