The invention discloses a long period grating based glass-based optical sensor. A glass-based buried waveguide layer includes a glass-based buried waveguide substrate, a glass-based buried waveguide core layer and an upper cladding from bottom to top in sequence. The glass-based optical sensor is characterized in that a long period metal grating film layer covers the upper cladding to form the periodic gratings, wherein the period T of the long period metal grating film layer satisfies the condition beta1-beta2=2pi/T. When the optical waves transmitting in the buried waveguide pass through the metal grating film layer, the metal grating film layer carries out total reflection, and part of the energy is transferred to the surface plasma waves on the interfaces between the metal and the tested substances. When the phases of the surface plasma waves are the same as the phases of the optical waveguide modes, the surface plasma waves are excited. Through testing the output end of the waveguide, the peak value curves of the surface plasma waves are obtained and then the characteristics of the tested samples are obtained. The glass-based optical sensor not only maintains easy miniaturization and stability but also lowers the cost, and can be used in such fields as medical diagnosis, environmental monitoring, biotechnology and food safety, etc.