An explicit MPS algorithm is much faster to analyze free surface flow than the traditional semi-implicit algorithm. However, validation of the algorithm has not been studied enough. This paper shows comparisons about numerical stability and accuracy of pressure the between explicit and semi-implicit MPS in a hydrostatic pressure problem and a dam break problem. Pressure oscillations by the explicit MPS is as the same lebel as those of the semi-implicit MPS. In the hydrostatic pressure problem, the time average of pressure is equal to its theoretical value. With Mach number 0.2, compressibility is about 1.0 percent from the initial state. It is shown by both of the calculation and theory. The explicit MPS is as accurate as the semi-implicit MPS with less calculation costs.