The invention provides position adjusting structures of a straddle type rail beam support. The position adjusting structures are arranged at the two sides of the rail beam support and are arranged ona base plate for fixing the rail beam support. Each position adjusting structure is composed of a push plate, a position adjusting bolt and a gap adjusting gasket assembly, wherein a groove matched with the push plate is formed in the base plate, the push plate is fixedly inlaid in the groove of the base plate, a threaded hole for enabling the position adjusting bolt to penetrate through the pushplate is formed in the transverse direction of the push plate, the position adjusting bolt is pushed on the rail beam support, and a gap between the push plate and the rail beam support is filled withthe gap adjusting gasket assembly. An adjusting mode that bolts push for adding or reducing gaskets is adopted to realize the position adjusting function of the support, and the safety and reliability of structure stress and the convenience of installation construction and later maintenance of the support can be effectively improved.