AbstractAlthough truck cranes commonly employ outriggers for the horizontal attitude adjustment prior to operation, the time-varying operation of the upper-structure, e.g., telescoping, pitching, rotating, loading and unloading, constantly influences the attitude stability of the chassis. In extreme operating conditions, a tiny attitude change can have disastrous consequences, resulting tip-over accidents. Although there are monitoring and warning systems of the chassis attitude in practice, the research on its active control is rarely seen. In response to this, a synchronous control theory of the upper operation and the chassis attitude maintenance were proposed. First, the expression of the center of mass of a typical truck crane was built according to its mechanism and motion parameters. Then, the quasi-static load bearing model of the outrigger system was built in combination with the deformation compatibility condition, by which the mathematical relationship between the upper operation and chassis attitude disturbance, i.e., the compensatory length of each outrigger that is required to maintain the attitude stationary of the chassis, can be determined. Based on the above models, the tip-over early warning model of truck cranes was deduced, and a synchronous control strategy of time-varying upper operation and chassis attitude maintenance was proposed and preliminarily verified by tests based on an electromechanical experimental platform. Results showed that the attitude stability of the chassis is improved by about 80% after control, which is beneficial to improve the safety of the truck crane, the operating efficiency, and reduce the operating burden of the driver.