A wideband antenna which has a structure of an equilateral triangular slot ring with a pair of branch slots is proposed. Based on the principle of multi-mode resonance, the antenna feed is set in the non-symmetrical position of the triangular slot ring, and the two branch slots are added symmetrically to the triangular slot ring in order to form many resonance circuits. Therefore, multi-mode resonance is obtained and the bandwidth of the antenna is improved. The results of simulation and measurement are basically consistent. The measured impedance bandwidth of the antenna is 2.11-3.32 GHz, |S11|<-10 dB, and the relative bandwidth reaches 44.5%. Within the impedance bandwidth, the antenna radiation performance is good, and the direction pattern is basically the same. The antenna can be applied in LTE 40 and 41 wireless communication systems, and the triangular slot ring structure can provide some reference for the research of wideband slot microstrip antenna.