In this article, a novel ultra-wideband four-way power divider based on spoof surface plasmon polaritons (SSPPs) is proposed. The study of the transition structure indicates that the wave supported by unilateral SSPPs possesses the similar dispersion relation to the ones restricted by bilateral SSPPs and effective transmission of electromagnetic wave can be realized in this structure. Owning to these features, waves propagating along the bilateral SSPPs can be equally divided into two unilateral SSPPs and the power divider can be realized by loading this structure, which solves the problem of power distribution in multi-way or even arbitrary ways. With the help of HFSS, the microstrip-fed power divider is simulated and results show that it performs well. In order to verify the simulation effect, a object is fabricated and the measured results are in good agreement with simulation results. This power divider has the advantages of ultra-wideband, low insertion loss and arbitrary-way of power distribution, which opens up a new avenue for the application of SSPPs in power divider and has a great application prospects in photonics integrated circuits.