Magnetic reconnection is thought to be a key process in most of solar eruptions. Thanks to high-resolution observations and simulations, the studied scale of reconnection process has become smaller and smaller. Spectroscopic observations show that the reconnection site can be very small, which always exhibits a bright core and two extended wings with fast speeds, i.e., transition-region explosive events. In this paper, using the PLUTO code, we perform a 2-D magnetohydrodynamic simulation to investigate the small-scale reconnection in double current sheets. Based on our simulation results, such as the line-of-sight velocity, number density and plasma temperature, we can synthesize the line profile of Si IV 1402.77 A which is a well known emission line to study the transition-region explosive events on the Sun. The synthetic line profile of Si IV 1402.77 A is complex with a bright core and two broad wings which can extend to be nearly 200 km/s. Our simulation results suggest that the transition-region explosive events on the Sun are produced by plasmoid instability during the small-scale magnetic reconnection.