容器是个好东西

采用弹性布局即可。

wxml:

<view class="form_item">
      <radio-group class='radio-group'>
        <view class="radio">
          <label>
            <radio value="America" color="#359ce7">
              美国
            </radio>
          </label>
        </view>
        <view class="radio">
          <label>
            <radio value="China" color="#359ce7">
              中国
            </radio>
          </label>
        </view>
                <view class="radio">
          <label>
            <radio value="Brazil" color="#359ce7">
             巴西
            </radio>
          </label>
        </view>
      </radio-group>
    </view>

wxss:

.form_item {
  display: flex;
  align-items: center;
  height: 38px;
  }

.radio-group {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: space-around;
  }

自定义呗