A signal adjustment method for a photoplethysmographic apparatus, comprising following steps: sampling background light data and mixed light data; determining whether the background light data falls within a preset background light data range, and/or determining whether calculated actual effective light data falls within a preset first effective light data range, wherein the actual effective light data is a difference between the mixed light data and the background light data; and in response to the background light data being beyond the preset background light data range, or the actual effective light data being beyond the preset first effective light data range, performing a light adjustment operation, wherein the light adjustment operation comprises: determining an estimated current transfer ratio based on a preset CTR or an actual CTR of the PPG apparatus; estimating a drive current required by a light source of the PPG apparatus and a gain required by an analog front end based on a drive current of the light source, a gain of the AFE, and the sampled background light data and mixed light data; calculating estimated effective light data of the PPG apparatus based on the estimated drive current required by the light source, the estimated gain required by the AFE, and the estimated CTR; and determining whether the estimated effective light data falls within a preset second effective light data range; and in response to the estimated effective light data falling within the preset second effective light data range, generating a to-be-adjusted current/gain value based on the estimated drive current required by the light source and gain required by the AFE, so as to adjust the drive current of the light source of the PPG apparatus and the gain of the AFE. sampling background light data and mixed light data; determining whether the background light data falls within a preset background light data range, and/or determining whether calculated actual effective light data falls within a preset first effective light data range, wherein the actual effective light data is a difference between the mixed light data and the background light data; and in response to the background light data being beyond the preset background light data range, or the actual effective light data being beyond the preset first effective light data range, performing a light adjustment operation, wherein the light adjustment operation comprises: determining an estimated current transfer ratio based on a preset CTR or an actual CTR of the PPG apparatus; estimating a drive current required by a light source of the PPG apparatus and a gain required by an analog front end based on a drive current of the light source, a gain of the AFE, and the sampled background light data and mixed light data; calculating estimated effective light data of the PPG apparatus based on the estimated drive current required by the light source, the estimated gain required by the AFE, and the estimated CTR; and determining whether the estimated effective light data falls within a preset second effective light data range; and in response to the estimated effective light data falling within the preset second effective light data range, generating a to-be-adjusted current/gain value based on the estimated drive current required by the light source and gain required by the AFE, so as to adjust the drive current of the light source of the PPG apparatus and the gain of the AFE. determining an estimated current transfer ratio based on a preset CTR or an actual CTR of the PPG apparatus; estimating a drive current required by a light source of the PPG apparatus and a gain required by an analog front end based on a drive current of the light source, a gain of the AFE, and the sampled background light data and mixed light data; calculating estimated effective light data of the PPG apparatus based on the estimated drive current required by the light source, the estimated gain required by the AFE, and the estimated CTR; and determining whether the estimated effective light data falls within a preset second effective light data range; and in response to the estimated effective light data falling within the preset second effective light data range, generating a to-be-adjusted current/gain value based on the estimated drive current required by the light source and gain required by the AFE, so as to adjust the drive current of the light source of the PPG apparatus and the gain of the AFE.