The invention belongs to a chemical quantitative analysis method, and relates to a quantitative liquid analysis method by spectrum baseline correction, which aims to overcome the defects of long test time, high cost and large test result error of the prior art. The method comprises the following steps of: (1) data acquisition, comprising the steps of selecting an apparatus, setting parameters, firstly testing spectroscopic data without a sample, and secondly testing samples; (2) spectrum baseline correction, comprising the steps of figuring out a linear representation coefficient by optimizing a constraint model and acquiring a baseline-free spectrum according to the linear representation coefficient, thereby implementing the spectrum correction; (3) model building, comprising the step of building a quantitative analysis model by taking a sample with known concentration as a training sample through partial least squares; and (4) quantitative analysis, comprising the step of transmitting a sample with unknown concentration into the model, and computing to obtain a quantitative analysis result. The method has the advantages that the quantitative analysis of liquid materials does not need complex sample pretreatment; the test cost is low; the test speed is high, and the method is suitable for online testing; and the quantitative analysis result is exact and reliable.