In this paper, exploding foil overpressure actuator was used to experimentally study the law of detonation wave collision in small-size charge conditions. In order to quantitatively study the growth, propagation, and duration of the ultrahigh-pressure phenomenon created by the detonation wave collision, photon doppler velocimetry was used to measure the pressure value of the detonation waves. And, further tests were conducted to isolate and measure the duration and pressure trend of this phenomenon by height gradient experiments. Meanwhile, the influence of two-point initiation and four-point initiation on the ultra-pressure value were compared. The results indicated that with the increase of explosive height, the colliding wave would undergo a regular oblique reflection to Mach reflection and finally to attenuation. This paper lays a foundation for the multipoint initiation of insensitive explosive and shaped charge.