Intravenous morphine is a controversial treatment for acute heart failure (AHF). This study aimed to evaluate and compare the efficacy of intravenous morphine treatment vs. no morphine treatment in AHF patients. Relevant research conducted before June 2020 was retrieved from electronic databases. One unpublished study of our own was also included. Studies were eligible for inclusion if they compared AHF patients treated with intravenous morphine and patients who did not receive morphine. This meta-analysis included three propensity-matched cohorts and two retrospective analyses, involving a total of 149,967 patients (intravenous-morphine group, n = 22,072; no-morphine group, n = 127,895). There was a non-significant increase in the in-hospital mortality in the morphine group (combined odds ratio [OR] = 2.14, 95% confidence interval [CI]: 0.88–5.23, p = 0.095, I{}^{\mathrm{2}} = 97.1%). However, subgroup analyse showed that the rate of in-hospital mortality with odds of 1.41 times more likely (95% CI: 1.11–1.80, p = 0.005, I{}^{\mathrm{2}} = 0%) in those receiving vs. not receiving intravenous morphine. No significant correlation was found between intravenous morphine and invasive mechanical ventilation (OR = 2.19, 95% CI: 0.84–5.73, p = 0.10, I{}^{\mathrm{2}} = 94.2%; subgroup analysis: OR = 2.24, 95% CI: 0.70–7.21, p = 0.176, I{}^{\mathrm{2}} = 95.1%) or long-term mortality (hazard ratio = 1.15, 95% CI: 0.96–1.34, p = 0.335; I{}^{\mathrm{2}} = 8.6%). The administration of intravenous morphine to patients with AHF may be related to in-hospital mortality, but not to invasive mechanical ventilation and long-term mortality.