In order to investigate the critical energy criterion of covered explosive detonated by cylindrical fragment impacting, a new equivalent model was made based on the rod criterion and one-dimensional initiation criterion. The initiation progress of covered explosive impacting by fragment is dealt as an equivalent to the progress of bared explosive by the method of theoretical calculation. Critical energy criterion contained with the length, diameter of the fragment and the thickness of the shell was deduced. Numerical simulation was done by software to validate the correctness of the conclusion. The results show that: the shock wave initiation is the main mechanism of explosive detonation while the explosive covered with thin shell, and the results of numerical simulation and theoretical calculation are basically the same, the critical energy criterion is applicable to the explosive covered with thin shell detonated by cylindrical fragment. And the L/D ratio has little effect on the critical detonation velocity while the L/D ratio is greater than the critical value.