The invention discloses a client online charging method and system, and an online charging gateway and relates to the field of online charging. The method and system realize a client online charging scheme through audio-form confirmation information. A client calls an audio interface at a bottom layer to play the audio-form confirmation information while no memory or video memory needs to be occupied. Even if a comparatively large quantity of terminal resources are occupied, the confirmation information can still be played normally and a condition that the confirmation information is slow in display or cannot be displayed does not happen, and the data size of the confirmation information in the form of an audio file is smaller compared to that in the form of a picture file: audio-form confirmation information is usually smaller than 1k and picture-form confirmation information is usually more than 1k, or even a dozen k. Therefore, transmission of the audio-form confirmation information is usually faster. The online charging efficiency is higher and user experience is better.