In order to enhance the multi-object detecting and tracking capability， a four-beam millimeter wave frequency scanning leaky wave antenna （LWA） based on spoof surface plasmon polaritons （SSPP） has been proposed. According to the theory of sinusoidally modulated reactance superposing surface （SMRSS）， Quad-beam LWA is realized by etching periodical slots on the top surface of substrate integrated waveguide （SIW）， and uniform slots etched on the bottom layer is used to eliminate the open-stopband effect. The measurement shows that the four beams can scan from -52° to 22° within the frequency band from 29 GHz to 30.2 GHz， achieving a total of 74° scanning range， and the beam scanning is up to 18°/%BW， which not only saves the spectrum source but improvs the multi-target detection efficiency.