System and method for analysing the gas present in the interannular space in tubular solar receivers (PCT/ES2016/070250) The invention relates to a non-invasive method and system for evaluation of the state of vacuum and detection of the type of gas present in the interannular cavity of receiver tubes (1) arranged in cylindro-parabolic collectors. The method comprises the ignition of a plasma in the annular cavity of said receiver tube (1), and the subsequent evaluation of the spectrum emitted by the excited plasma by means of an optical analysis subsystem. The system according to the invention also comprises a radiofrequency source (2), an impedance coupler (3) and a radiofrequency applicator (4) by which means radiofrequency energy is applied to the glass outer cover (1») of the tube (1). The optical analysis subsystem is provided with a spectrometer (7) which is connected to a computer (10) and carries out the analysis of the spectrum of the gas present in the receiver tube (1)..