On-chip Si3N4 microcavities composed of multi-mode waveguides can achieve high-quality factor and anomalous dispersion simultaneously, which is necessary for solitons generation. It has been proven to be a promising platform for compact optical (Kerr) frequency comb generation. To further reduce the threshold power for generating a single soliton microcomb, a racetrack Si3N4 microcavity with Euler bends is reported. Compared with traditional racetrack microcavities, Euler bending can significantly suppress the sudden change in bending radius at the waveguide connection, which suppresses mode interactions and reduces propagation losses, resulting in an increase in Q factor value. Based on this racetrack microcavity, using the auxiliary laser heating method, a single soliton frequency comb with a repetition rate of 34 GHz and a 3 dB bandwidth exceeding 18 nm (corresponding to a pulse duration of 143 fs) can be generated using only a 19 mW pump laser (estimated on-chip pump power below 10 mW). The optimized racetrack microcavities can be building blocks for integrated photonics systems.