public static float getProcessCpuRate()
    {
        
        float totalCpuTime1 = getTotalCpuTime();
        float processCpuTime1 = getAppCpuTime();
        try
        {
            Thread.sleep(360);
            
        }
        catch (Exception e)
        {
        }
        
        float totalCpuTime2 = getTotalCpuTime();
        float processCpuTime2 = getAppCpuTime();
        
        float cpuRate = 100 * (processCpuTime2 - processCpuTime1)
                / (totalCpuTime2 - totalCpuTime1);
        
        return cpuRate;
    }
    
    public static long getTotalCpuTime()
    { // 获取系统总CPU使用时间
        String[] cpuInfos = null;
        try
        {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    new FileInputStream("/proc/stat")), 1000);
            String load = reader.readLine();
            reader.close();
            cpuInfos = load.split(" ");
        }
        catch (IOException ex)
        {
            ex.printStackTrace();
        }
        long totalCpu = Long.parseLong(cpuInfos[2])
                + Long.parseLong(cpuInfos[3]) + Long.parseLong(cpuInfos[4])
                + Long.parseLong(cpuInfos[6]) + Long.parseLong(cpuInfos[5])
                + Long.parseLong(cpuInfos[7]) + Long.parseLong(cpuInfos[8]);
        return totalCpu;
    }
    
    public static long getAppCpuTime()
    { // 获取应用占用的CPU时间
        String[] cpuInfos = null;
        try
        {
            int pid = android.os.Process.myPid();
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    new FileInputStream("/proc/" + pid + "/stat")), 1000);
            String load = reader.readLine();
            reader.close();
            cpuInfos = load.split(" ");
        }
        catch (IOException ex)
        {
            ex.printStackTrace();
        }
        long appCpuTime = Long.parseLong(cpuInfos[13])
                + Long.parseLong(cpuInfos[14]) + Long.parseLong(cpuInfos[15])
                + Long.parseLong(cpuInfos[16]);
        return appCpuTime;
    }

计算某个时间段内AppCpuTime与TotalCpuTime的变化，然后按照比例换算成该应用的Cpu使用率。

Android系统本省也有一个类是用来显示Cpu使用率的：

Android获取应用cpu使用率,布布扣,bubuko.com

Android获取应用cpu使用率