Abstract: Frame is an important concept in wavelet transform. First of all, the concept of frame is analyzed, and a reasonable definition is introduced with definite physical meaning. Then a simple proof of sufficient and necessary criterion for orthogonal frame is presented. After that, by making use of dual basis, the general reconstruction formula about frame is discussed, and the computation formula for the dual frame is presented, in which no operators are contained. The fact that there are no operators in the formula of dual frame is of great practical importance for signal processing, and of great help in understanding the concept “frame”. Finally, some important problems about frame are pointed out by analyzing some simple examples.