The invention discloses a method for measuring a single-crystal-silicon-based solar surface antireflection film by a reflection spectrum. The method comprises the following steps: carrying out modeling analog computation to obtain total reflection efficiency A of a single-crystal-silicon-based solar cell with an antireflection film and total reflection efficiency B of a single-crystal-silicon-based solar cell without an antireflection film respectively; working out a relative reflection ratio Rcal of the single-crystal-silicon-based solar cell based on the total reflection efficiency A and the total reflection efficiency B; measuring a reflection ratio R of the single-crystal-silicon-based solar cell with the antireflection film relative to the single-crystal-silicon-based solar cell without the antireflection film; comparing the relative reflection ratio Rcal with the reflection ratio R, setting an optical constant of an antireflection film thickness and an antireflection film material or a coefficient of an optical constant physical model as a variable in a model, and calculating through a numerical regression curve fitting process to obtain the optical constant of the film thickness and the material. According to the method, the accuracy of measuring the characteristics of a silicon-based solar sample film by a reflectivity measurement method is improved, the application field of a spectral reflectometer is expanded, and measured hardware is relatively simple in structure and relatively low in cost.