The invention discloses a power amplifier circuit and a loudspeaker system, and relates to the technical field of loudspeakers. The power amplifier circuit is used for driving a loudspeaker and comprises a voltage detection module, wherein the voltage detection module is used for detecting voltage of the loudspeaker; and the voltage detection module comprises a detection end which is arranged independently and is directly connected with the loudspeaker. The invention further discloses the loudspeaker system with the power amplifier circuit. The voltage detection module of the power amplifier circuit disclosed by the invention comprises the independently arranged detection end, and the detection end can be directly connected with the loudspeaker, so that influence of loop resistance to the voltage detection module can be reduced, the voltage detection module is enabled to precisely detect voltage of two ends of the loudspeaker, the detection precision of the power amplifier circuit is greatly improved, and furthermore adjusting accuracy of the power amplifier circuit to the loudspeaker is improved; and moreover the power amplifier circuit has the advantages of simple structure, convenience in implementation and good stability.