Microseismic imaging plays an important role in hydraulic fracture detection, and the first-arrival picking of microseismic events is the bedrock of microseismic imaging. Manual picking is the most reliable and also the most time-consuming method for the detection of the first arrival of microseismic events. Accurate and efficient first-arrival picking in a real noisy environment is a challenge for most of the automatic first-arrival picking methods. We have developed a novel workflow to automatically pick the first arrival of microseismics by using a state-of-the art pixel-wise convolutional image segmentation method. We first form the training data by randomly selecting part of the microseismic traces and manually pick the time index of the first arrivals. Next, we segment the selected traces into two parts according to the time index of manual picking and assign each part a label accordingly. Then, we build an encoder-decoder convolutional neural network architecture and use the training data and training label as the input. Next, we obtain the trained network hierarchy by learning the segmented training data and labels. Finally, we predict the first arrivals of microseismic events by applying the trained network hierarchy to the rest of the microseismic traces. The synthetic and field data examples demonstrate that our method successfully identifies the first arrivals. The predicted first-arrival result obtained by using our method is superior to the result obtained by using the traditional method of short-term average and long-term average.