Objective To evaluate the safety and efficacy of potassium and magnesium supplement with potassium aspartate and magnesium aspartate injection in gastrointestinal surgery patients during absolute fasting．Methods A multicenter randomized controlled clinical trial was conducted in 111 patients after gastrointestinal surgery. For trial group，56 patients were given potassium aspartate and magnesium aspartate injection （Panangin®） in half of the total potassium replenished dose and the rest half of the potassium replenished dose was given in 10% potassium chloride injection．For control group，55 patients were given 10% potassium chloride injection for the total dose of potassium replenished．Such treatments maintained five consecutive days after surgical operation．Clinical observations were performed until patients were discharged from the hospitals．Results Before the intervention，there were no significant differences for the baseline between two groups （P＞0.05）．There was no significant difference for the serum potassium level between two groups （P＞0.05） after intervention．The amount of urinary potassium （mmol/24 h） for patients in the trial group was significantly lower than that in the control group during treatment after operation．The serum magnesium level of control group was much lower than that of control group （P＜0.05）. In the clinical observation process，no drug-related adverse event was observed．Conclusions The supplementary effect of potassium and magnesium for potassium aspartate and magnesium aspartate injection in patients with gastrointestinal surgery during absolute fasting is significant，and superior to potassium chloride injection for potassium supplement．Potassium aspartate and magnesium aspartate injection is a safe and appropriate choice for patients with potassium depletion．