Soft rubber exhibits good adhesive ability, excellent vibrational absorption, and high traction for tribological use. However, rubber wear particles induced by rapid wear of soft rubber are serious problems under special conditions, which could negatively influence the equipment running, the environment, and even human health faster. This paper presents the influence of five variables (the load, velocity, humidity, slip ratio, and braking time) on the emission of tyre wear particle matter (TWPM), which are generated by soft butadiene-styrene rubber tyres against the concrete under braking conditions with a self-developed rolling-contact test machine. The emission quantity of TWPM and their relationships with the rubber wear mechanism were investigated. The results show that the emission quantity and increment of TWPM of 3.0 μm in size (TWPM 3.0) are much greater than those of TWPMs 5.0 and 10.0. Humidity and braking time both have negative correlations with the quantity of TWPM 3.0, while load, velocity, and slip ratio have positive correlations. Abrasive rubber wear results in more severely TWPM emission than fatigue wear does. It is easy for the soft rubber to form Schallamach pattern on its surface and induce severe abrasive wear, which potentially produces more TWPMs. The variables exhibit the following order of influence on the emission of TWPM 3.0: load, slip ratio, velocity, braking time, and humidity. The impact factor of the load is approximately twice as high as that of velocity and slip ratio and three times greater than that of humidity and braking deceleration. This study provides a comprehensive understanding of the generation of TWPMs of soft rubber.