The invention discloses an energy-saving effect monitoring and evaluating method and system based on fuel consumption of a vehicle. The method comprises the following steps: before the vehicle uses an energy-saving product, collecting miles of travel S1, fuel consumption data Q1 and device state of the vehicle within one time period T; after the vehicle uses the energy-saving product, collecting miles of travel S2, fuel consumption data Q2 and device state of the vehicle within the same time period T; based on difference of the device state of the vehicle before and after using the energy-saving product, carrying out compensation on the fuel consumption data obtained before the vehicle uses the energy-saving product; calculating fuel consumption parameters within unit time and fuel consumption parameters within unit mile before or after the vehicle uses the energy-saving product; and calculating fuel-saving parameters within unit time and fuel-saving parameters within unit mile, and realizing monitoring and evaluation of the energy-saving effect according to the fuel-saving parameters. The method and system realize monitoring and evaluation of the energy-saving effect brought by the energy-saving product based on fuel consumption of the vehicle, and facilitate optimization and selection of the energy-saving products.