Synchronization at receiver, including mode detection, frame synchronization, sampling time recovery (STR) and carrier frequency synchronization four parts, is crucial for digital communication systems. Time domain synchronous (TDS) block transmission system, in which pseudo noise (PN) sequences are padded between two adjacent data blocks as guard intervals (GI), is widely used in wireless communication and terrestrial digital TV broadcasting. In order to form several modes for the different requirements, the GI length and the padding sequences are usually designed. However, GI padding methods in traditional TDS block transmission incurs usually tremendous complexity in mode detection and mode extension, and the four parts of synchronization are usually separated, which are unsuitable for burst transmission systems. In this paper, a signal frame structure for TDS block transmission is proposed to support scalable GI padding and a joint synchronization scheme is presented accordingly, where multiple correlation outputs based on different local sequences can be directly used for joint synchronization. Moreover, timing error and carrier frequency offset can be estimated from any two correlation peaks in each frame or adjacent frames to guide symbol timing recovery and carrier frequency synchronization. Both the analysis and simulation show the proposed scheme is effective and results in low-complexity joint synchronization at receiver side.