In order to solve the problem of pressure and temperature back propagation in twostage pulse detonation engine, this paper proposes two different kinds of jet nozzles with several planks or bosses. And with hydrogen as fuel and air as oxidizer, detonation initiation with different planks or bosses is simulated. The results indicate that detonation can be initiated when the number of planks is 3 or 4. When the number of bosses is 3, 4 or 5, detonation can be initiated successfully. When the number of planks or bosses is 4, the detonation initiation effect is the best by shock wave focusing, and the effect of preventing pressure and temperature back propagation is also well. On the whole the effects of planks or bosses on preventing pressure and temperature back propagation is very limited.