The invention discloses a single-channel collection device and method for modulating multi-channel signals through bioelectricity and sine waves. The collection device collects N-channel biomedical signals through a single-channel analog-digital converter, and high-frequency sine waves loaded with PPG signals and low-frequency bioelectric signals are included. Current signals are converted into preset amplitude voltage signals through a current/voltage conversion amplifier. Preset amplitude bioelectric signals are obtained through a bioelectric signal detection circuit. After the preset amplitude voltage signals and the preset amplitude bioelectric signals are added through an additive operation circuit, mixed signals are obtained. The mixed signals are converted into digital signals through the single-channel analog-digital converter. A microprocessor processes the digital signals, so modulated sine wave signals and low-frequency bioelectric signals are obtained through separation, and multi-channel PPG signals are obtained through demodulation from the modulated sine wave signals. The collection device can synchronously collect the multi-channel biomedical signals through the single-channel analog-digital converter and has the advantages that the circuits are simple, the cost is low, and measurement is accurate.