<p>Internal solitary waves (ISWs) have considerable energy to drive the mixing of water masses in the Sulu Sea. The propagation speed is one of the critical parameters in quantifying the energy budget of the ISWs. We collected 1 354 groups of ISWs’ speeds from tandem satellite remote sensing images with temporal intervals shorter than 25 min and analyzed their spatial and multi-scale temporal variations in the Sulu Sea. We found that water depth plays an important role in modulating the spatial variation of wave speeds, which increase exponentially with water depth with a power of 0.26. Tidal currents, ocean stratification, background circulation, and climate affect the temporal variations of wave speeds from days to months or years. The fortnightly spring/neap tidal currents cause daily variations of wave speeds up to 40% by modulating the ISW amplitudes. In addition to the well-accepted results that monthly variations of wave speeds are related to density stratification, we found that enhanced stratification increases wave speeds, and the background circulation leads to a maximum decrease of 0.27 m/s in the linear counterparts of wave speed. Moreover, the averaged wave speed collected in October is lower than the corresponding linear one possibly due to some unknown dynamical processes or underestimation of background current. As for the interannual variations, we show that wave speed increases in La Niña years and decreases in El Niño years as a result of the climatic modulation on the depth of the maximum value of buoyancy frequency.</p>