The invention discloses a two-dimensional computable target detection, recognition and identification performance predicting method. The method comprises the following steps of: using a polynomial or an exponential function as a curve fitting function, selecting a sample image database of specific imaging parameters for fitting to obtain a detection/recognition/identification probability computational formula, and adopting the formula to compute and obtain the detection/recognition/identification probability of a measured image. The method overcomes the subjectivity, randomness and non-repeatability of the current Johnson rule, the subjective judgment of people is approximately realized through the computer algorithm, and the operability is strong.