The invention discloses a large dynamic range magnetic field measurement system and a measurement method. The measurement system comprises an SQUID sensor, a polarity transform module, a single pole double throw switch, a signal compression acquisition module, a control circuit and a power supply. The SQUID sensor is connected with the polarity transform module. The polarity transform module is connected with the signal compression acquisition module through the single pole double throw switch. The breakover direction of the single pole double throw switch is controlled by the control circuit. The power supply powers corresponding modules. The measurement method comprises the steps that 1 a secondary field signal is received; 2 the signal accesses the input end of an in-phase follower and an anti-phase follower; 3 polarity transformation is carried out on the secondary field signal; 4 form conversion is carried out the secondary field signal; 5 the second field signal is compressed; and 6 the second field signal is acquired. The measurement system and the measurement method have the advantages that the problem that the effective dynamic range of the existing analog-to-digital converter cannot realize large dynamic range magnetic field measurement is solved.