A micro-electromechanical systems pump includes a first substrate, a first oxide layer, a second substrate, and a piezoelectric element. The first oxide layer is stacked on the first substrate. The second substrate is combined with the first substrate, and the second substrate includes a silicon wafer layer, a second oxide layer, and a silicon material layer. The silicon wafer layer has an actuation portion. The actuation portion is circular and has a maximum stress value and an actuation stress value. The second oxide layer is formed on the silicon wafer layer. The silicon material layer is located at the second oxide layer and is combined with the first oxide layer. The piezoelectric element is stacked on the actuation portion, and has a piezoelectric stress value. The maximum stress value is greater than the actuation stress value, and the actuation stress value is greater than the piezoelectric stress value.