While the nanowire (NW) lasers have attracted much attentions as nanoscale coherent sources in recent years, the heat accumulation and temperature-rise-induced breakdown remain challenges to improving the lasers for practical applications. Here we propose a microscale liquid-cooled approach to address the issue. Calculated results show that, compared with conventional air-cooled lasing systems, liquid-cooled NW lasers can allow much higher thermal power. By keeping the NW temperature below 373 K, the allowed thermal power in water is about 21 times that in air (850 µW in water versus 40 µW in air). Transient temperature evolution reveals a much faster heat dissipation of the NW in water (30 ns) than in air (7 µs), indicating a much higher allowable repetition rate in water than in air (e.g., 10 MHz versus 100 kHz). Our results suggest a possible route to compact NW lasers with higher power, new materials and new operation modes.