Abstract: Digital beam forming(DBF) is special for phased array ultrasonic transducer compared to other ultrasonic nondestructive testing and is also the kernel technology of the whole signal-receiving system. By the merits of field programmable gate array( FPGA), exact time-delay and fast adding of signals multiplied by weighting factors were achieved through modules based FPGA. Dynamic focusing of received signals in different directions and depths was also achieved. Good DBF was realized.