The invention relates to the technical field of pipe jacking machines, in particular to a variable diameter rectangular pipe jacking machine shield. The variable diameter rectangular pipe jacking machine shield adopts modularization design, and each single shield base module comprises an independent drive mechanism mounting seat, a motor mounting seat and a correction oil cylinder structure. The shield base modules of the variable diameter rectangular pipe jacking machine shield are divided into peripherical shield base modules and middle shield base modules, and the peripherical shield base modules and the middle shield base modules can be combined into a rectangular pipe jacking machine of needed dimension through module connection. The modules are connected by using high-strength bolts,and whole circle seal rings are arranged on connection surfaces of the modules. The variable diameter rectangular pipe jacking machine shield effectively avoids the problems that a new rectangular pipe jacking machine shield needs to be designed if a tunnel of sectional dimension different from an existing tunnel needs to be excavated, the new rectangular pipe jacking machine is long in customization period and high in customization cost, and therefore prolonging of a construction period and increase of construction cost are caused.