The invention provides an adjustable pressurization system of serial-parallel boilers of big and small turbochargers, comprising a high-pressure stage turbine by-pass pipeline by-pass valve, a high-pressure stage turbine by-pass pipeline, a high-pressure stage turbine, a high-pressure and low-pressure turbine connection pipeline flow rate switching control valve, a high-pressure and low-pressure turbine connection pipeline, a low-pressure stage turbine by-pass pipeline, a low-pressure stage turbine, a steam output pipe system, a main steam turbine, a fume purification device, a high-pressure stage compressor by-pass pipeline by-pass valve, a high-pressure stage compressor by-pass pipeline, a high-pressure stage compressor, a high-pressure and low-pressure compressor connection pipeline flow rate switching control valve, a high-pressure and low-pressure compressor connection pipeline, a low-pressure stage compressor by-pass pipeline, an auxiliary steam turbine, a speed changing mechanism 1, a speed changing mechanism 2, a fuel oil supply system, a boiler water supply mechanism, an air conditioning baffle plate and a low-pressure stage compressor. The variation range of the equivalent weight circulation area of the turbine is wider, thereby the operation matching of a booster set and the boiler is improved and the purpose of optimizing the economy of the boiler is achieved.