In view of the problem that in the existing methods some effect factors are ill considered which lead up to the calculation results deviating from the fact, an improved calculation method of detection probability of aircraft for sky-wave radar is put forward, and the impact of different ionosphere states on detection distance of sky-wave radar is concluded. Taking the variety of target RCS with gesture during flight through given track into account, a calculation model of target dynamic RCS is established. On this basis, the detection probability of aircraft for sky-wave radar can be gotten by using the models of instantaneous detection probability and the comprehensive detection probability. The results show that ionosphere state of Es blanket leads to a decrease in target detection probability by 0.273. And the values of target detection probability are in great difference under the conditions of the different tracks and gestures, and the maximal different value reaches to 0.253. The feasibility and the validity of the method are verified by using living examples.