The invention discloses a portable on-line detection device for a vehicular direct-current electric energy meter. The portable on-line detection device comprises a shell, a PCB (Printed Circuit Board), an external bus, a power supply model, a power calculation module, a data processing module and an error detection module, wherein the external bus is in data connection with the power calculation module and the error detection module respectively; the power supply module, the power calculation module, the data processing module and the error detection module are arranged on the PCB; the PCB is mounted in the shell; the power calculation module sends collected current and voltage of a power battery and power calculated according to the current and the voltage to the data processing module; the error detection module is used for detecting and sending an electric energy error pulse output of the portable on-line detection device and an electric energy error input of the vehicular electric energy meter to the data processing module; the data processing module obtains an error value of the electric energy meter through data processing. Compared with an existing detection means, the portable on-line detection device can be used for realizing the on-line detection of the error of the vehicular electric energy meter; the electric energy meter does not need to be disassembled to be subsequently detected; further, the entire detection time is short; the operation is simple.