Abstract: Through the dynamic load simulating system and simulating model tests of roof structure, the general load distribution law on the mined key roof and its structure in shallow seam under thick sandy soil overburden was deduced, and the load variation law on key block A, B and C of roof structure were revealed. Furthermore, the load transmitting mechanism of the reformed “unloading arch” was found in periodic loading on roof, then the new concept of load transmitting factor was put forward, and the amendatory model of M. M. Promojiyfakonov arch combined with that of K. Terzaghi was set up. On such a basis, the formula of lithology factor and time factor of load transmitting was established.