The invention discloses a measurement method for a thickness of a coating of a steel plate. The method comprises the steps of measuring an outer diameter R of a steel coil formed by strip steel with acoating, an inner diameter R0 of the steel coil, a length L of the strip steel for forming the steel coil and a thickness T of the strip steel; and obtaining a thickness T of the coating on the basis of a formula as shown in the specification, wherein unit parameters of the outer diameter R, the inner diameter R0, the length L, the thickness T of the strip steeland the thickness T of the coating all are the same. The invention further discloses a measurement system adopted by the measurement method for the thickness of the coating of the steel plate. The measurement system comprises a strip steel thickness measurement device, a strip steel length measurement device, a steel coil size measurement device and a control device, wherein the strip steel thickness measurement device is arranged upstream of a coating machine along the transmission direction of the strip steel and is used for measuring the thickness T of the strip steel; the strip steel length measurement device is used for measuring the length L of the strip steel for forming the steel coil; the steel coil size measurement device is used for measuring the outer diameter R of the steel coil and the inner diameter R0 of the steel coil; the control device is connected with the strip steel thickness measurement device, the strip steel length measurement device andthe steel coil size measurement device separately to receive transmitted data and to calculate and output the thickness T of the coating.